Covalent Bonding And Molecular Structure Name Per Date: Fill & Download for Free

Mercury (element)From Wikipedia, the free encyclopediaFor other uses, see Mercury (disambiguation).Mercury,80HgSpectral lines of mercury (UV not seen)General propertiesName, symbolmercury, HgPronunciation/ˈmɜːrkjəri/mer-kyə-reeAppearancesilveryMercury in the periodic tableCd↑Hg↓Cngold ← mercury → thalliumAtomic number (Z)80Group, blockgroup 12, d-blockPeriodperiod 6Element categorytransition metal, alternatively considered a post-transition metalStandard atomic weight (Ar)200.592(3)[1]Electron configuration[Xe] 4f145d106s2Electrons per shell2, 8, 18, 32, 18, 2Physical propertiesPhaseliquidMelting point234.3210 K ​(−38.8290 °C, ​−37.8922 °F)Boiling point629.88 K ​(356.73 °C, ​674.11 °F)Density near r.t.13.534 g/cm3Triple point234.3156 K, ​1.65×10−7kPaCritical point1750 K, 172.00 MPaHeat of fusion2.29 kJ/molHeat of vaporization59.11 kJ/molMolar heat capacity27.983 J/(mol·K)Vapor pressureP(Pa)1101001 k10 k100 katT(K)315350393449523629Atomic propertiesOxidation states2 (mercuric), 1 (mercurous), −2 ​(a mildly basic oxide)ElectronegativityPauling scale: 2.00Ionization energies1st: 1007.1 kJ/mol2nd: 1810 kJ/mol3rd: 3300 kJ/molAtomic radiusempirical: 151 pmCovalent radius132±5 pmVan der Waals radius155 pmMiscellaneaCrystal structure​rhombohedralSpeed of soundliquid: 1451.4 m/s (at 20 °C)Thermal expansion60.4 µm/(m·K) (at 25 °C)Thermal conductivity8.30 W/(m·K)Electrical resistivity961 nΩ·m (at 25 °C)Magnetic orderingdiamagnetic[2]Magnetic susceptibility(χmol)−33.44·10−6cm3/mol (293 K)[3]CAS Number7439-97-6HistoryDiscoveryAncient Chinese and Indians (before 2000 BCE)Main isotopes of mercuryisoNAhalf-lifeDMDE (MeV)DP194Hgsyn444 yε0.040194Au195Hgsyn9.9 hε1.510195Au196Hg0.15%is stable with 116 neutrons197Hgsyn64.14 hε0.600197Au198Hg10.04%is stable with 118 neutrons199Hg16.94%is stable with 119 neutrons200Hg23.14%is stable with 120 neutrons201Hg13.17%is stable with 121 neutrons202Hg29.74%is stable with 122 neutrons203Hgsyn46.612 dβ−0.492203Tl204Hg6.82%is stable with 124 neutronsviewtalkedit| references | in WikidataMercury is a chemical element with symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named hydrargyrum (/haɪˈdrɑːrdʒərəm/).[4]A heavy, silvery d-block element, mercury is the only metallic element that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature.Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). The red pigment vermilion is obtained by grinding natural cinnabar or synthetic mercuric sulfide.Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, fluorescent lamps and other devices, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favor of alternatives such as alcohol- or galinstan-filled glass thermometers and thermistor- or infrared-based electronic instruments. Likewise, mechanical pressure gauges and electronic strain gauge sensors have replaced mercury sphygmomanometers. Mercury remains in use in scientific research applications and in amalgam for dental restoration in some locales. It is used in fluorescent lighting. Electricity passed through mercury vapor in a fluorescent lamp produces short-wave ultraviolet light which then causes the phosphor in the tube to fluoresce, making visible light.Mercury poisoning can result from exposure to water-soluble forms of mercury (such as mercuric chloride or methylmercury), by inhalation of mercury vapor, or by ingesting any form of mercury.Contents[hide]1Properties1.1Physical properties1.2Chemical properties1.3Isotopes2Etymology3History4Occurrence5Chemistry5.1Compounds of mercury(I)5.2Compounds of mercury(II)5.3Possibility of higher oxidation states5.4Organomercury compounds6Applications6.1Medicine6.2Production of chlorine and caustic soda6.3Laboratory uses6.4Niche uses6.5Firearms6.6Historic uses7Toxicity and safety7.1Releases in the environment7.2Occupational exposure7.3Fish8Regulations8.1International8.2United States8.3European Union8.4Norway8.5Sweden8.6Denmark9See also10References11Further reading12External linksPropertiesPhysical propertiesA pound coin (density ~7.6 g/cm3) floats in mercury due to the combination of the buoyant force and surface tension.Mercury is a heavy, silvery-white liquid metal. Compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity.[5]It has a freezing point of −38.83 °C and a boiling point of 356.73 °C,[6][7][8]both the lowest of any metal.[9]Upon freezing, the volume of mercury decreases by 3.59% and its density changes from 13.69 g/cm3when liquid to 14.184 g/cm3when solid. The coefficient of volume expansion is 181.59 × 10−6at 0 °C, 181.71 × 10−6at 20 °C and 182.50 × 10−6at 100 °C (per °C). Solid mercury is malleable and ductile and can be cut with a knife.[10]A complete explanation of mercury's extreme volatility delves deep into the realm of quantum physics, but it can be summarized as follows: mercury has a unique electron configuration where electrons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d, and 6s subshells. Because this configuration strongly resists removal of an electron, mercury behaves similarly to noble gases, which form weak bonds and hence melt at low temperatures.The stability of the 6s shell is due to the presence of a filled 4f shell. An f shell poorly screens the nuclear charge that increases the attractive Coulomb interaction of the 6s shell and the nucleus (see lanthanide contraction). The absence of a filled inner f shell is the reason for the somewhat higher melting temperature of cadmium and zinc, although both these metals still melt easily and, in addition, have unusually low boiling points.[6][7]Chemical propertiesMercury does not react with most acids, such as dilute sulfuric acid, although oxidizing acids such as concentrated sulfuric acid and nitric acid or aqua regia dissolve it to give sulfate, nitrate, and chloride. Like silver, mercury reacts with atmospheric hydrogen sulfide. Mercury reacts with solid sulfur flakes, which are used in mercury spill kits to absorb mercury (spill kits also use activated carbon and powdered zinc).[11]AmalgamsMercury-discharge spectral calibration lampMercury dissolves many other metals such as gold and silver to form amalgams. Iron is an exception, and iron flasks have traditionally been used to trade mercury. Several other first row transition metals with the exception of manganese, copper and zinc are reluctant to form amalgams. Other elements that do not readily form amalgams with mercury include platinum.[12][13]Sodium amalgam is a common reducing agent in organic synthesis, and is also used in high-pressure sodium lamps.Mercury readily combines with aluminium to form a mercury-aluminium amalgam when the two pure metals come into contact. Since the amalgam destroys the aluminium oxide layer which protects metallic aluminium from oxidizing in-depth (as in iron rusting), even small amounts of mercury can seriously corrode aluminium. For this reason, mercury is not allowed aboard an aircraft under most circumstances because of the risk of it forming an amalgam with exposed aluminium parts in the aircraft.[14]Mercury embrittlement is the most common type of liquid metal embrittlement.IsotopesMain article: Isotopes of mercuryThere are seven stable isotopes of mercury with 202Hg being the most abundant (29.86%). The longest-lived radioisotopes are 194Hg with a half-life of 444 years, and 203Hg with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day. 199Hg and 201Hg are the most often studied NMR-active nuclei, having spins of  1⁄2 and  3⁄2 respectively.[5]EtymologyHg is the modern chemical symbol for mercury. It comes from hydrargyrum, a Latinized form of the Greek word ὑδράργυρος (hydrargyros), which is a compound word meaning "water-silver" (from ὑδρ- hydr-, the root of ὕδωρ, "water," and ἄργυρος argyros "silver") – since it is liquid like water and shiny like silver. The element was named after the Roman god Mercury, known for his speed and mobility. It is associated with the planet Mercury; the astrological symbol for the planet is also one of the alchemical symbols for the metal; the Sanskrit word for alchemy is Rasavātam which means "the way of mercury".[15]Mercury is the only metal for which the alchemical planetary name became the common name.[16]HistoryThe symbol for the planet Mercury (☿) has been used since ancient times to represent the elementMercury was found in Egyptian tombs that date from 1500 BC.[17]Daedalus used quicksilver to install voice in his moving statues.[18][19]In China and Tibet, mercury use was thought to prolong life, heal fractures, and maintain generally good health, although it is now known that exposure to mercury vapor leads to serious adverse health effects.[20]The first emperor of China, Qín Shǐ Huáng Dì—allegedly buried in a tomb that contained rivers of flowing mercury on a model of the land he ruled, representative of the rivers of China—was killed by drinking a mercury and powdered jade mixture formulated by Qin alchemists (causing liver failure, mercury poisoning, and brain death) who intended to give him eternal life.[21][22]Khumarawayh ibn Ahmad ibn Tulun, the second Tulunid ruler of Egypt (r. 884–896), known for his extravagance and profligacy, reportedly built a basin filled with mercury, on which he would lie on top of air-filled cushions and be rocked to sleep.[23]In November 2014 "large quantities" of mercury were discovered in a chamber 60 feet below the 1800-year-old pyramid known as the "Temple of the Feathered Serpent," "the third largest pyramid of Teotihuacan," Mexico along with "jade statues, jaguar remains, a box filled with carved shells and rubber balls."[24]The ancient Greeks used cinnabar (mercury sulfide) in ointments; the ancient Egyptians and the Romans used it in cosmetics. In Lamanai, once a major city of the Maya civilization, a pool of mercury was found under a marker in a Mesoamerican ballcourt.[25][26]By 500 BC mercury was used to make amalgams (Medieval Latin amalgama, "alloy of mercury") with other metals.[27]Alchemists thought of mercury as the First Matter from which all metals were formed. They believed that different metals could be produced by varying the quality and quantity of sulfur contained within the mercury. The purest of these was gold, and mercury was called for in attempts at the transmutation of base (or impure) metals into gold, which was the goal of many alchemists.[16]The mines in Almadén (Spain), Monte Amiata (Italy), and Idrija (now Slovenia) dominated mercury production from the opening of the mine in Almadén 2500 years ago, until new deposits were found at the end of the 19th century.[28]OccurrenceSee also: Category:Mercury minerals and Category:Mercury minesMercury output in 2005Mercury is an extremely rare element in Earth's crust, having an average crustal abundance by mass of only 0.08 parts per million (ppm).[29]Because it does not blend geochemically with those elements that constitute the majority of the crustal mass, mercury ores can be extraordinarily concentrated considering the element's abundance in ordinary rock. The richest mercury ores contain up to 2.5% mercury by mass, and even the leanest concentrated deposits are at least 0.1% mercury (12,000 times average crustal abundance). It is found either as a native metal (rare) or in cinnabar, corderoite, livingstonite and other minerals, with cinnabar (HgS) being the most common ore.[30]Mercury ores usually occur in very young orogenic belts where rocks of high density are forced to the crust of Earth,[citation needed]often in hot springs or other volcanic regions.[31]Beginning in 1558, with the invention of the patio process to extract silver from ore using mercury, mercury became an essential resource in the economy of Spain and its American colonies. Mercury was used to extract silver from the lucrative mines in New Spain and Peru. Initially, the Spanish Crown's mines in Almadén in Southern Spain supplied all the mercury for the colonies.[32]Mercury deposits were discovered in the New World, and more than 100,000 tons of mercury were mined from the region of Huancavelica, Peru, over the course of three centuries following the discovery of deposits there in 1563. The patio process and later pan amalgamation process continued to create great demand for mercury to treat silver ores until the late 19th century.[33]Native mercury with cinnabar, Socrates mine, Sonoma County, California. Cinnabar sometimes alters to native mercury in the oxidized zone of mercury deposits.Former mines in Italy, the United States and Mexico, which once produced a large proportion of the world supply, have now been completely mined out or, in the case of Slovenia (Idrija) and Spain (Almadén), shut down due to the fall of the price of mercury. Nevada's McDermitt Mine, the last mercury mine in the United States, closed in 1992. The price of mercury has been highly volatile over the years and in 2006 was $650 per 76-pound (34.46 kg) flask.[34]Mercury is extracted by heating cinnabar in a current of air and condensing the vapor. The equation for this extraction isHgS + O2→ Hg + SO2In 2005, China was the top producer of mercury with almost two-thirds global share followed by Kyrgyzstan.[35]Several other countries are believed to have unrecorded production of mercury from copper electrowinning processes and by recovery from effluents.Because of the high toxicity of mercury, both the mining of cinnabar and refining for mercury are hazardous and historic causes of mercury poisoning.[36]In China, prison labor was used by a private mining company as recently as the 1950s to develop new cinnabar mines. Thousands of prisoners were used by the Luo Xi mining company to establish new tunnels.[37]Worker health in functioning mines is at high risk.The European Union directive calling for compact fluorescent bulbs to be made mandatory by 2012 has encouraged China to re-open cinnabar mines to obtain the mercury required for CFL bulb manufacture. Environmental dangers have been a concern, particularly in the southern cities of Foshan and Guangzhou, and in Guizhou province in the southwest.[37]Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabar calcines. Water run-off from such sites is a recognized source of ecological damage. Former mercury mines may be suited for constructive re-use. For example, in 1976 Santa Clara County, California purchased the historic Almaden Quicksilver Mine and created a county park on the site, after conducting extensive safety and environmental analysis of the property.[38]ChemistrySee also: Category:Mercury compoundsMercury exists in two main oxidation states, I and II.Compounds of mercury(I)Unlike its lighter neighbors, cadmium and zinc, mercury usually forms simple stable compounds with metal-metal bonds. Most mercury(I) compounds are diamagnetic and feature the dimeric cation, Hg2+2. Stable derivatives include the chloride and nitrate. Treatment of Hg(I) compounds complexation with strong ligands such as sulfide, cyanide, etc. induces disproportionation to Hg2+and elemental mercury.[39]Mercury(I) chloride, a colorless solid also known as calomel, is really the compound with the formula Hg2Cl2, with the connectivity Cl-Hg-Hg-Cl. It is a standard in electrochemistry. It reacts with chlorine to give mercuric chloride, which resists further oxidation. Mercury(I) hydride, a colorless gas, has the formula HgH, containing no Hg-Hg bond.Indicative of its tendency to bond to itself, mercury forms mercury polycations, which consist of linear chains of mercury centers, capped with a positive charge. One example is Hg2+3(AsF−6)2.[40]Compounds of mercury(II)Mercury(II) is the most common oxidation state and is the main one in nature as well. All four mercuric halides are known. They form tetrahedral complexes with other ligands but the halides adopt linear coordination geometry, somewhat like Ag+does. Best known is mercury(II) chloride, an easily sublimating white solid. HgCl2forms coordination complexes that are typically tetrahedral, e.g. HgCl2−4.Mercury(II) oxide, the main oxide of mercury, arises when the metal is exposed to air for long periods at elevated temperatures. It reverts to the elements upon heating near 400 °C, as was demonstrated by Joseph Priestley in an early synthesis of pure oxygen.[11]Hydroxides of mercury are poorly characterized, as they are for its neighbors gold and silver.Being a soft metal, mercury forms very stable derivatives with the heavier chalcogens. Preeminent is mercury(II) sulfide, HgS, which occurs in nature as the ore cinnabar and is the brilliant pigment vermillion. Like ZnS, HgS crystallizes in two forms, the reddish cubic form and the black zinc blende form.[5]Mercury(II) selenide (HgSe) and mercury(II) telluride (HgTe) are also known, these as well as various derivatives, e.g. mercury cadmium telluride and mercury zinc telluride being semiconductors useful as infrared detector materials.[41]Mercury(II) salts form a variety of complex derivatives with ammonia. These include Millon's base (Hg2N+), the one-dimensional polymer (salts of HgNH+2)n), and "fusible white precipitate" or [Hg(NH3)2]Cl2. Known as Nessler's reagent, potassium tetraiodomercurate(II) (HgI2−4) is still occasionally used to test for ammonia owing to its tendency to form the deeply colored iodide salt of Millon's base.Mercury fulminate is a detonator widely used in explosives.[5]Possibility of higher oxidation statesOxidation states above +2 in an uncharged species are extremely rare, although a cyclic mercurinium(IV) cation, with three substituents, may be an intermediate in oxymercuration reactions.[42][43]In 2007, a report of synthesis of a mercury(IV) compound, mercury(IV) fluoride, was published,[44]but later experiments could not replicate the synthesis.[45]In the 1970s, there was a claim on synthesis of a mercury(III) compound, but it is now thought to be false.[46]Organomercury compoundsMain article: Organomercury compoundOrganic mercury compounds are historically important but are of little industrial value in the western world. Mercury(II) salts are a rare example of simple metal complexes that react directly with aromatic rings. Organomercury compounds are always divalent and usually two-coordinate and linear geometry. Unlike organocadmium and organozinc compounds, organomercury compounds do not react with water. They usually have the formula HgR2, which are often volatile, or HgRX, which are often solids, where R is aryl or alkyl and X is usually halide or acetate. Methylmercury, a generic term for compounds with the formula CH3HgX, is a dangerous family of compounds that are often found in polluted water.[47]They arise by a process known as biomethylation.ApplicationsThe bulb of a mercury-in-glass thermometerMercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic applications. It is used in some thermometers, especially ones which are used to measure high temperatures. A still increasing amount is used as gaseous mercury in fluorescent lamps, while most of the other applications are slowly phased out due to health and safety regulations and is in some applications replaced with less toxic but considerably more expensive Galinstan alloy.[48]MedicineSee also: Amalgam (dentistry)Amalgam fillingMercury and its compounds have been used in medicine, although they are much less common today than they once were, now that the toxic effects of mercury and its compounds are more widely understood. The first edition of the Merck's Manual featured many mercuric compounds[49]such as:MercauroMercuro-iodo-hemol.Mercury-ammonium chlorideMercury BenzoateMercuricMercury Bichloride (Corrosive Mercuric Chloride, U.S.P.)Mercury ChlorideMild Mercury CyanideMercury SuccinimideMercury IodideRed Mercury BiniodideMercury IodideYellow Mercury Proto-iodideBlack (Hahnemann), Soluble Mercury OxideRed Mercury OxideYellow Mercury OxideMercury SalicylateMercury SuccinimideMercury Imido-succinateMercury SulphateBasic Mercury Subsulphate; Turpeth MineralMercury TannateMercury-Ammonium ChlorideMercury is an ingredient in dental amalgams. Thiomersal (called Thimerosal in the United States) is an organic compound used as a preservative in vaccines, though this use is in decline.[50]Thiomersal is metabolized to ethyl mercury. Although it was widely speculated that this mercury-based preservative could cause or trigger autism in children, scientific studies showed no evidence supporting any such link.[51]Nevertheless, thiomersal has been removed from, or reduced to trace amounts in all U.S. vaccines recommended for children 6 years of age and under, with the exception of inactivated influenza vaccine.[52]Another mercury compound, merbromin (Mercurochrome), is a topical antiseptic used for minor cuts and scrapes that is still in use in some countries.Mercury in the form of one of its common ores, cinnabar, is used in various traditional medicines, especially in traditional Chinese medicine. Review of its safety has found that cinnabar can lead to significant mercury intoxication when heated, consumed in overdose, or taken long term, and can have adverse effects at therapeutic doses, though effects from therapeutic doses are typically reversible. Although this form of mercury appears to be less toxic than other forms, its use in traditional Chinese medicine has not yet been justified, as the therapeutic basis for the use of cinnabar is not clear.[53]Today, the use of mercury in medicine has greatly declined in all respects, especially in developed countries. Thermometers and sphygmomanometers containing mercury were invented in the early 18th and late 19th centuries, respectively. In the early 21st century, their use is declining and has been banned in some countries, states and medical institutions. In 2002, the U.S. Senate passed legislation to phase out the sale of non-prescription mercury thermometers. In 2003, Washington and Maine became the first states to ban mercury blood pressure devices.[54]Mercury compounds are found in some over-the-counter drugs, including topical antiseptics, stimulant laxatives, diaper-rash ointment, eye drops, and nasal sprays. The FDA has "inadequate data to establish general recognition of the safety and effectiveness" of the mercury ingredients in these products.[55]Mercury is still used in some diuretics although substitutes now exist for most therapeutic uses.Production of chlorine and caustic sodaChlorine is produced from sodium chloride (common salt, NaCl) using electrolysis to separate the metallic sodium from the chlorine gas. Usually the salt is dissolved in water to produce a brine. By-products of any such chloralkali process are hydrogen (H2) and sodium hydroxide (NaOH), which is commonly called caustic soda or lye. By far the largest use of mercury[56][57]in the late 20th century was in the mercury cell process (also called the Castner-Kellner process) where metallic sodium is formed as an amalgam at a cathode made from mercury; this sodium is then reacted with water to produce sodium hydroxide.[58]Many of the industrial mercury releases of the 20th century came from this process, although modern plants claimed to be safe in this regard.[57]After about 1985, all new chloralkali production facilities that were built in the United States used membrane cell or diaphragm cell technologies to produce chlorine.Laboratory usesSome medical thermometers, especially those for high temperatures, are filled with mercury; they are gradually disappearing. In the United States, non-prescription sale of mercury fever thermometers has been banned since 2003.[59]Mercury is also found in liquid mirror telescopes.Some transit telescopes use a basin of mercury to form a flat and absolutely horizontal mirror, useful in determining an absolute vertical or perpendicular reference. Concave horizontal parabolic mirrors may be formed by rotating liquid mercury on a disk, the parabolic form of the liquid thus formed reflecting and focusing incident light. Such telescopes are cheaper than conventional large mirror telescopes by up to a factor of 100, but the mirror cannot be tilted and always points straight up.[60][61][62]Liquid mercury is a part of popular secondary reference electrode (called the calomel electrode) in electrochemistry as an alternative to the standard hydrogen electrode. The calomel electrode is used to work out the electrode potential of half cells.[63]Last, but not least, the triple point of mercury, −38.8344 °C, is a fixed point used as a temperature standard for the International Temperature Scale (ITS-90).[5]In polarography both the dropping mercury electrode[64]and the hanging mercury drop electrode[65]use elemental mercury. This use allows a new uncontaminated electrode to be available for each measurement or each new experiment.Niche usesGaseous mercury is used in mercury-vapor lamps and some "neon sign" type advertising signs and fluorescent lamps. Those low-pressure lamps emit very spectrally narrow lines, which are traditionally used in optical spectroscopy for calibration of spectral position. Commercial calibration lamps are sold for this purpose; reflecting a fluorescent ceiling light into a spectrometer is a common calibration practice.[66]Gaseous mercury is also found in some electron tubes, including ignitrons, thyratrons, and mercury arc rectifiers.[67]It is also used in specialist medical care lamps for skin tanning and disinfection.[68]Gaseous mercury is added to cold cathode argon-filled lamps to increase the ionization and electrical conductivity. An argon-filled lamp without mercury will have dull spots and will fail to light correctly. Lighting containing mercury can be bombarded/oven pumped only once. When added to neon filled tubes the light produced will be inconsistent red/blue spots until the initial burning-in process is completed; eventually it will light a consistent dull off-blue color.[69]The deep violet glow of a mercury vapor discharge in a germicidal lamp, whose spectrum is rich in invisible ultraviolet radiation.Skin tanner containing a low-pressure mercury vapor lamp and two infrared lamps, which act both as light source and electrical ballastAssorted types of fluorescent lamps.CosmeticsMercury, as thiomersal, is widely used in the manufacture of mascara. In 2008, Minnesota became the first state in the United States to ban intentionally added mercury in cosmetics, giving it a tougher standard than the federal government.[70]A study in geometric mean urine mercury concentration identified a previously unrecognized source of exposure (skin care products) to inorganic mercury among New York City residents. Population-based biomonitoring also showed that mercury concentration levels are higher in consumers of seafood and fish meals.[71]FirearmsA mercury compound called "Mercury(II) fulminate" is a primary explosive which is mainly used as a primer of a cartridge in firearms.Historic usesA Single-Pole, Single-Throw (SPST) mercury switch.Mercury manometer to measure pressureMany historic applications made use of the peculiar physical properties of mercury, especially as a dense liquid and a liquid metal:Quantities of liquid mercury ranging from 90 to 600 grams (3.2 to 21.2 oz) have been recovered from elite Maya tombs (100-700AD)[24] or ritual caches at six sites. This mercury may have been used in bowls as mirrors for divinatory purposes. Five of these date to the Classic Period of Maya civilization (c. 250–900) but one example predated this.[72]In Islamic Spain, it was used for filling decorative pools. Later, the American artist Alexander Calder built a mercury fountain for the Spanish Pavilion at the 1937 World Exhibition in Paris. The fountain is now on display at the Fundació Joan Miró in Barcelona.[73]Mercury was used inside wobbler lures. Its heavy, liquid form made it useful since the lures made an attractive irregular movement when the mercury moved inside the plug. Such use was stopped due to environmental concerns, but illegal preparation of modern fishing plugs has occurred.The Fresnel lenses of old lighthouses used to float and rotate in a bath of mercury which acted like a bearing.[74]Mercury sphygmomanometers (blood pressure meter), barometers, diffusion pumps, coulometers, and many other laboratory instruments. As an opaque liquid with a high density and a nearly linear thermal expansion, it is ideal for this role.[75]As an electrically conductive liquid, it was used in mercury switches (including home mercury light switches installed prior to 1970), tilt switches used in old fire detectors, and tilt switches in some home thermostats.[76]Owing to its acoustic properties, mercury was used as the propagation medium in delay line memory devices used in early digital computers of the mid-20th century.Experimental mercury vapor turbines were installed to increase the efficiency of fossil-fuel electrical power plants.[77] The South Meadow power plant in Hartford, CT employed mercury as its working fluid, in a binary configuration with a secondary water circuit, for a number of years starting in the late 1920s in a drive to improve plant efficiency. Several other plants were built, including the Schiller Station in Portsmouth, NH, which went online in 1950. The idea did not catch on industry-wide due to the weight and toxicity of mercury, as well as the advent of supercritical steam plants in later years.[78][79]Similarly, liquid mercury was used as a coolant for some nuclear reactors; however, sodium is proposed for reactors cooled with liquid metal, because the high density of mercury requires much more energy to circulate as coolant.[80]Mercury was a propellant for early ion engines in electric space propulsion systems. Advantages were mercury's high molecular weight, low ionization energy, low dual-ionization energy, high liquid density and liquid storability at room temperature. Disadvantages were concerns regarding environmental impact associated with ground testing and concerns about eventual cooling and condensation of some of the propellant on the spacecraft in long-duration operations. The first spaceflight to use electric propulsion was a mercury-fueled ion thruster developed by NASA Lewis and flown on the Space Electric Rocket Test "SERT-1" spacecraft launched by NASA at its Wallops Flight Facility in 1964. The SERT-1 flight was followed up by the SERT-2 flight in 1970. Mercury and caesium were preferred propellants for ion engines until Hughes Research Laboratory performed studies finding xenon gas to be a suitable replacement. Xenon is now the preferred propellant for ion engines as it has a high molecular weight, little or no reactivity due to its noble gas nature, and has a high liquid density under mild cryogenic storage.[81][82]Others applications made use of the chemical properties of mercury:The mercury battery is a non-rechargeable electrochemical battery, a primary cell, that was common in the middle of the 20th century. It was used in a wide variety of applications and was available in various sizes, particularly button sizes. Its constant voltage output and long shelf life gave it a niche use for camera light meters and hearing aids. The mercury cell was effectively banned in most countries in the 1990s due to concerns about the mercury contaminating landfills.[83]Mercury was used for preserving wood, developing daguerreotypes, silvering mirrors, anti-fouling paints (discontinued in 1990), herbicides (discontinued in 1995), handheld maze games, cleaning, and road leveling devices in cars. Mercury compounds have been used in antiseptics, laxatives, antidepressants, and in antisyphilitics.It was allegedly used by allied spies to sabotage Luftwaffe planes: a mercury paste was applied to bare aluminium, causing the metal to rapidly corrode; this would cause structural failures.[84]Chloralkali process: The largest industrial use of mercury during the 20th century was in electrolysis for separating chlorine and sodium from brine; mercury being the anode of the Castner-Kellner process. The chlorine was used for bleaching paper (hence the location of many of these plants near paper mills) while the sodium was used to make sodium hydroxide for soaps and other cleaning products. This usage has largely been discontinued, replaced with other technologies that utilize membrane cells.[85]As electrodes in some types of electrolysis, batteries (mercury cells), sodium hydroxide and chlorine production, handheld games, catalysts, insecticides.Mercury was once used as a gun barrel bore cleaner.[86][87]From the mid-18th to the mid-19th centuries, a process called "carroting" was used in the making of felt hats. Animal skins were rinsed in an orange solution (the term "carroting" arose from this color) of the mercury compound mercuric nitrate, Hg(NO3)2·2H2O.[88] This process separated the fur from the pelt and matted it together. This solution and the vapors it produced were highly toxic. The United States Public Health Service banned the use of mercury in the felt industry in December 1941. The psychological symptoms associated with mercury poisoning inspired the phrase "mad as a hatter". Lewis Carroll's "Mad Hatter" in his book Alice's Adventures in Wonderland was a play on words based on the older phrase, but the character himself does not exhibit symptoms of mercury poisoning.[89]Gold and silver mining. Historically, mercury was used extensively in hydraulic gold mining in order to help the gold to sink through the flowing water-gravel mixture. Thin gold particles may form mercury-gold amalgam and therefore increase the gold recovery rates.[5] Large-scale use of mercury stopped in the 1960s. However, mercury is still used in small scale, often clandestine, gold prospecting. It is estimated that 45,000 metric tons of mercury used in California for placer mining have not been recovered.[90] Mercury was also used in silver mining.[91]Historic medicinal usesMercury(I) chloride (also known as calomel or mercurous chloride) has been used in traditional medicine as a diuretic, topical disinfectant, and laxative. Mercury(II) chloride (also known as mercuric chloride or corrosive sublimate) was once used to treat syphilis (along with other mercury compounds), although it is so toxic that sometimes the symptoms of its toxicity were confused with those of the syphilis it was believed to treat.[92]It is also used as a disinfectant. Blue mass, a pill or syrup in which mercury is the main ingredient, was prescribed throughout the 19th century for numerous conditions including constipation, depression, child-bearing and toothaches.[93]In the early 20th century, mercury was administered to children yearly as a laxative and dewormer, and it was used in teething powders for infants. The mercury-containing organohalide merbromin (sometimes sold as Mercurochrome) is still widely used but has been banned in some countries such as the U.S.[94]Toxicity and safetySee also: Mercury poisoning and Mercury cycleMercury and most of its compounds are extremely toxic and must be handled with care; in cases of spills involving mercury (such as from certain thermometers or fluorescent light bulbs), specific cleaning procedures are used to avoid exposure and contain the spill.[95]Protocols call for physically merging smaller droplets on hard surfaces, combining them into a single larger pool for easier removal with an eyedropper, or for gently pushing the spill into a disposable container. Vacuum cleaners and brooms cause greater dispersal of the mercury and should not be used. Afterwards, fine sulfur, zinc, or some other powder that readily forms an amalgam (alloy) with mercury at ordinary temperatures is sprinkled over the area before itself being collected and properly disposed of. Cleaning porous surfaces and clothing is not effective at removing all traces of mercury and it is therefore advised to discard these kinds of items should they be exposed to a mercury spill.Mercury can be absorbed through the skin and mucous membranes and mercury vapors can be inhaled, so containers of mercury are securely sealed to avoid spills and evaporation. Heating of mercury, or of compounds of mercury that may decompose when heated, should be carried out with adequate ventilation in order to minimize exposure to mercury vapor. The most toxic forms of mercury are its organic compounds, such as dimethylmercury and methylmercury. Mercury can cause both chronic and acute poisoning.Releases in the environmentAmount of atmospheric mercury deposited at Wyoming's Upper Fremont Glacier over the last 270 yearsPreindustrial deposition rates of mercury from the atmosphere may be about 4 ng /(1 L of ice deposit). Although that can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric source by 4–6 times.[96]Natural sources, such as volcanoes, are responsible for approximately half of atmospheric mercury emissions. The human-generated half can be divided into the following estimated percentages:[97][98][99]65% from stationary combustion, of which coal-fired power plants are the largest aggregate source (40% of U.S. mercury emissions in 1999). This includes power plants fueled with gas where the mercury has not been removed. Emissions from coal combustion are between one and two orders of magnitude higher than emissions from oil combustion, depending on the country.[97]11% from gold production. The three largest point sources for mercury emissions in the U.S. are the three largest gold mines. Hydrogeochemical release of mercury from gold-mine tailings has been accounted as a significant source of atmospheric mercury in eastern Canada.[100]6.8% from non-ferrous metal production, typically smelters.6.4% from cement production.3.0% from waste disposal, including municipal and hazardous waste, crematoria, and sewage sludge incineration.3.0% from caustic soda production.1.4% from pig iron and steel production.1.1% from mercury production, mainly for batteries.2.0% from other sources.The above percentages are estimates of the global human-caused mercury emissions in 2000, excluding biomass burning, an important source in some regions.[97]Recent atmospheric mercury contamination in outdoor urban air was measured at 0.01–0.02 µg/m3. A 2001 study measured mercury levels in 12 indoor sites chosen to represent a cross-section of building types, locations and ages in the New York area. This study found mercury concentrations significantly elevated over outdoor concentrations, at a range of 0.0065 – 0.523 μg/m3. The average was 0.069 μg/m3.[101]Mercury also enters into the environment through the improper disposal (e.g., land filling, incineration) of certain products. Products containing mercury include: auto parts, batteries, fluorescent bulbs, medical products, thermometers, and thermostats.[102]Due to health concerns (see below), toxics use reduction efforts are cutting back or eliminating mercury in such products. For example, the amount of mercury sold in thermostats in the United States decreased from 14.5 tons in 2004 to 3.9 tons in 2007.[103]Most thermometers now use pigmented alcohol instead of mercury, and galinstan alloy thermometers are also an option. Mercury thermometers are still occasionally used in the medical field because they are more accurate than alcohol thermometers, though both are commonly being replaced by electronic thermometers and less commonly by galinstan thermometers. Mercury thermometers are still widely used for certain scientific applications because of their greater accuracy and working range.Historically, one of the largest releases was from the Colex plant, a lithium-isotope separation plant at Oak Ridge, Tennessee. The plant operated in the 1950s and 1960s. Records are incomplete and unclear, but government commissions have estimated that some two million pounds of mercury are unaccounted for.[104]A serious industrial disaster was the dumping of mercury compounds into Minamata Bay, Japan. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease.[105][106]Occupational exposureDue to the health effects of mercury exposure, industrial and commercial uses are regulated in many countries. The World Health Organization, OSHA, and NIOSH all treat mercury as an occupational hazard, and have established specific occupational exposure limits. Environmental releases and disposal of mercury are regulated in the U.S. primarily by the United States Environmental Protection Agency.Effects and symptoms of mercury poisoningMain article: Mercury poisoningToxic effects include damage to the brain, kidneys and lungs. Mercury poisoning can result in several diseases, including acrodynia (pink disease), Hunter-Russell syndrome, and Minamata disease.Symptoms typically include sensory impairment (vision, hearing, speech), disturbed sensation and a lack of coordination. The type and degree of symptoms exhibited depend upon the individual toxin, the dose, and the method and duration of exposure. Case control studies have shown effects such as tremors, impaired cognitive skills, and sleep disturbance in workers with chronic exposure to mercury vapor even at low concentrations in the range 0.7–42 μg/m3.[107][108]A study has shown that acute exposure (4 – 8 hours) to calculated elemental mercury levels of 1.1 to 44 mg/m3resulted in chest pain, dyspnea, cough, hemoptysis, impairment of pulmonary function, and evidence of interstitial pneumonitis.[109]Acute exposure to mercury vapor has been shown to result in profound central nervous system effects, including psychotic reactions characterized by delirium, hallucinations, and suicidal tendency. Occupational exposure has resulted in broad-ranging functional disturbance, including erethism, irritability, excitability, excessive shyness, and insomnia. With continuing exposure, a fine tremor develops and may escalate to violent muscular spasms. Tremor initially involves the hands and later spreads to the eyelids, lips, and tongue. Long-term, low-level exposure has been associated with more subtle symptoms of erethism, including fatigue, irritability, loss of memory, vivid dreams and depression.[110][111]TreatmentResearch on the treatment of mercury poisoning is limited. Currently available drugs for acute mercurial poisoning include chelators N-acetyl-D, L-penicillamine (NAP), British Anti-Lewisite (BAL), 2,3-dimercapto-1-propanesulfonic acid (DMPS), and dimercaptosuccinic acid (DMSA). In one small study including 11 construction workers exposed to elemental mercury, patients were treated with DMSA and NAP.[112]Chelation therapy with both drugs resulted in the mobilization of a small fraction of the total estimated body mercury. DMSA was able to increase the excretion of mercury to a greater extent than NAP.[113]FishMain article: Mercury in fishFish and shellfish have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury, a highly toxic organic compound of mercury. Species of fish that are high on the food chain, such as shark, swordfish, king mackerel, bluefin tuna, albacore tuna, and tilefish contain higher concentrations of mercury than others. As mercury and methylmercury are fat soluble, they primarily accumulate in the viscera, although they are also found throughout the muscle tissue.[114]When this fish is consumed by a predator, the mercury level is accumulated. Since fish are less efficient at depurating than accumulating methylmercury, fish-tissue concentrations increase over time. Thus species that are high on the food chain amass body burdens of mercury that can be ten times higher than the species they consume. This process is called biomagnification. Mercury poisoning happened this way in Minamata, Japan, now called Minamata disease.RegulationsInternational140 countries agreed in the Minamata Convention on Mercury by the United Nations Environment Programme (UNEP) to prevent emissions.[115]The convention was signed on 10 October 2013.[116]United StatesIn the United States, the Environmental Protection Agency is charged with regulating and managing mercury contamination. Several laws give the EPA this authority, including the Clean Air Act, the Clean Water Act, the Resource Conservation and Recovery Act, and the Safe Drinking Water Act. Additionally, the Mercury-Containing and Rechargeable Battery Management Act, passed in 1996, phases out the use of mercury in batteries, and provides for the efficient and cost-effective disposal of many types of used batteries.[117]North America contributed approximately 11% of the total global anthropogenic mercury emissions in 1995.[118]The United States Clean Air Act, passed in 1990, put mercury on a list of toxic pollutants that need to be controlled to the greatest possible extent. Thus, industries that release high concentrations of mercury into the environment agreed to install maximum achievable control technologies (MACT). In March 2005, the EPA promulgated a regulation[119]that added power plants to the list of sources that should be controlled and instituted a national cap and trade system. States were given until November 2006 to impose stricter controls, but after a legal challenge from several states, the regulations were struck down by a federal appeals court on 8 February 2008. The rule was deemed not sufficient to protect the health of persons living near coal-fired power plants, given the negative effects documented in the EPA Study Report to Congress of 1998.[120]However newer data published in 2015 showed that after introduction of the stricter controls mercury declined sharply, indicating that the Clean Air Act had its intended impact.[121]The EPA announced new rules for coal-fired power plants on 22 December 2011.[122]Cement kilns that burn hazardous waste are held to a looser standard than are standard hazardous waste incinerators in the United States, and as a result are a disproportionate source of mercury pollution.[123]European UnionIn the European Union, the directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (see RoHS) bans mercury from certain electrical and electronic products, and limits the amount of mercury in other products to less than 1000 ppm.[124]There are restrictions for mercury concentration in packaging (the limit is 100 ppm for sum of mercury, lead, hexavalent chromium and cadmium) and batteries (the limit is 5 ppm).[125]In July 2007, the European Union also banned mercury in non-electrical measuring devices, such as thermometers and barometers. The ban applies to new devices only, and contains exemptions for the health care sector and a two-year grace period for manufacturers of barometers.[126]NorwayNorway enacted a total ban on the use of mercury in the manufacturing and import/export of mercury products, effective 1 January 2008.[127]In 2002, several lakes in Norway were found to have a poor state of mercury pollution, with an excess of 1 µg/g of mercury in their sediment.[128]In 2008, Norway’s Minister of Environment Development Erik Solheim said: “Mercury is among the most dangerous environmental toxins. Satisfactory alternatives to Hg in products are available, and it is therefore fitting to induce a ban.”[129]SwedenProducts containing mercury were banned in Sweden in 2009.[130][131]DenmarkIn 2008, Denmark also banned dental mercury amalgam,[129]except for molar masticating surface fillings in permanent (adult) teeth.See alsoAmalgam (dentistry)Mercury poisoningMercury pollution in the oceanMethylmercuryMinamata diseaseRed mercuryReferencesJump up^ Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure Appl. Chem. 88 (3): 265–91. doi:10.1515/pac-2015-0305.Jump up^ "Mgnetic Susceptibility of the Elements And Inorganic Compounds" (PDF). The DZero Experiment. Fermi National Accelerator Laboratory: DØ Experiment (lagacy document). Archived from the original (PDF) on 2004-03-24. Retrieved 18 February 2015.Jump up^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.Jump up^ "hydrargyrum". Random House Webster's Unabridged Dictionary.^ Jump up to:a b c d e f Hammond, C. R The Elements in Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.^ Jump up to:a b Senese, F. "Why is mercury a liquid at STP?". General Chemistry Online at Frostburg State University. Retrieved 1 May 2007.^ Jump up to:a b Norrby, L.J. (1991). "Why is mercury liquid? Or, why do relativistic effects not get into chemistry textbooks?". Journal of Chemical Education. 68 (2): 110. Bibcode:1991JChEd..68..110N. doi:10.1021/ed068p110.Jump up^ Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. pp. 4.125–4.126. ISBN 0-8493-0486-5.Jump up^ "Dynamic Periodic Table". Dynamic Periodic Table. Retrieved 2016-11-22.Jump up^ Simons, E. N. (1968). Guide to Uncommon Metals. Frederick Muller. p. 111.^ Jump up to:a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.Jump up^ Gmelin, Leopold (1852). Hand book of chemistry. Cavendish Society. pp. 103 (Na), 110 (W), 122 (Zn), 128 (Fe), 247 (Au), 338 (Pt). Retrieved 30 December 2012.Jump up^ Soratur (2002). Essentials of Dental Materials. Jaypee Brothers Publishers. p. 14. ISBN 978-81-7179-989-3.Jump up^ Vargel, C.; Jacques, M.; Schmidt, M. P. (2004). Corrosion of Aluminium. Elsevier. p. 158. ISBN 9780080444956.Jump up^ Cox, R (1997). The Pillar of Celestial Fire. 1st World Publishing. p. 260. ISBN 1-887472-30-4.^ Jump up to:a b Stillman, J. M. (2003). Story of Alchemy and Early Chemistry. Kessinger Publishing. pp. 7–9. ISBN 978-0-7661-3230-6.Jump up^ "Mercury and the environment — Basic facts". Environment Canada, Federal Government of Canada. 2004. Retrieved 27 March 2008.Jump up^ The automatones of Greek Mythology online at the Theoi Project.Jump up^ Hyginus. Astronomica 2.1Jump up^ "Mercury — Element of the ancients". Center for Environmental Health Sciences, Dartmouth College. Retrieved 9 April 2012.Jump up^ "Qin Shihuang". Ministry of Culture, People's Republic of China. 2003. Retrieved 27 March 2008.Jump up^ Wright, David Curtis (2001). The History of China. Greenwood Publishing Group. p. 49. ISBN 0-313-30940-X.Jump up^ Sobernheim, Moritz (1987). "Khumārawaih". In Houtsma, Martijn Theodoor. E.J. Brill's first encyclopaedia of Islam, 1913–1936, Volume IV: 'Itk–Kwaṭṭa. Leiden: BRILL. p. 973. ISBN 90-04-08265-4.^ Jump up to:a b Yuhas, Alan (2015-04-24). "Liquid mercury found under Mexican pyramid could lead to king's tomb". The Guardian. ISSN 0261-3077. Retrieved 2016-11-22.Jump up^ Pendergast, David M. (6 August 1982). "Ancient maya mercury". Science. 217 (4559): 533–535. Bibcode:1982Sci...217..533P. doi:10.1126/science.217.4559.533. PMID 17820542.Jump up^ "Lamanai". Retrieved 17 June 2011.Jump up^ Hesse R W (2007). Jewelrymaking through history. Greenwood Publishing Group. p. 120. ISBN 0-313-33507-9.Jump up^ Eisler, R. (2006). Mercury hazards to living organisms. CRC Press. ISBN 978-0-8493-9212-2.Jump up^ Ehrlich, H. L.; Newman D. K. (2008). Geomicrobiology. CRC Press. p. 265. ISBN 978-0-8493-7906-2.Jump up^ Rytuba, James J. "Mercury from mineral deposits and potential environmental impact". Environmental Geology. 43 (3): 326–338. doi:10.1007/s00254-002-0629-5.Jump up^ "Mercury Recycling in the United States in 2000" (PDF). USGS. Retrieved 7 July 2009.Jump up^ Burkholder, M. & Johnson, L. (2008). Colonial Latin America. Oxford University Press. pp. 157–159. ISBN 0-19-504542-4.Jump up^ Jamieson, R W (2000). Domestic Architecture and Power. Springer. p. 33. ISBN 0-306-46176-5.Jump up^ Brooks, W. E. (2007). "Mercury" (PDF). U.S. Geological Survey. Retrieved 30 May 2008.Jump up^ World Mineral Production. London: British Geological Survey, NERC. 2001.Check date values in: |year= / |date= mismatch (help)Jump up^ About the Mercury Rule Archived 1 May 2012 at the Wayback Machine.. http://Act.credoaction.com (21 December 2011). Retrieved on 30 December 2012.^ Jump up to:a b Sheridan, M. (3 May 2009). "'Green' Lightbulbs Poison Workers: hundreds of factory staff are being made ill by mercury used in bulbs destined for the West". The Sunday Times (of London, UK).Jump up^ Boulland M (2006). New Almaden. Arcadia Publishing. p. 8. ISBN 0-7385-3131-6.Jump up^ Henderson, W. (2000). Main group chemistry. Great Britain: Royal Society of Chemistry. p. 162. ISBN 0-85404-617-8.Jump up^ Brown, I. D.; Gillespie, R. J.; Morgan, K. R.; Tun, Z.; Ummat, P. K. (1984). "Preparation and crystal structure of mercury hexafluoroniobate (Hg3NbF6) and mercury hexafluorotantalate (Hg3TaF6): mercury layer compounds". Inorganic Chemistry. 23 (26): 4506–4508. doi:10.1021/ic00194a020.Jump up^ Rogalski, A (2000). Infrared detectors. CRC Press. p. 507. ISBN 90-5699-203-1.Jump up^ Bamford, C.H.; Compton, R.G.; Tipper, C.F.H. (1973). Addition and Elimination Reactions of Aliphatic Compounds. Elsevier. pp. 49–. ISBN 978-0-444-41051-1.Jump up^ Carey, Francis A. & Sundberg, Richard J. (2007). Advanced Organic Chemistry: Part A: Structure and Mechanisms. Springer. pp. 517–. ISBN 978-0-387-44897-8.Jump up^ Wang, Xuefang; Andrews, Lester; Riedel, Sebastian; Kaupp, Martin (2007). "Mercury Is a Transition Metal: The First Experimental Evidence for HgF4". Angew. Chem. Int. Ed. 46 (44): 8371–8375. doi:10.1002/anie.200703710. PMID 17899620.Jump up^ "Is mercury a transition material? - University of Hull". Home | University of Hull. Retrieved 2016-11-22.Jump up^ Riedel, S.; Kaupp, M. (2009). "The Highest Oxidation States of the Transition Metal Elements" (PDF). Coordination Chemistry Reviews. 253 (5–6): 606–624. doi:10.1016/j.ccr.2008.07.014.[permanent dead link]Jump up^ National Research Council (U.S.) – Board on Environmental Studies and Toxicology (2000). Toxicological effects of methylmercury. National Academies Press. ISBN 978-0-309-07140-6.Jump up^ Surmann, P; Zeyat, H (November 2005). "Voltammetric analysis using a self-renewable non-mercury electrode". Analytical and Bioanalytical Chemistry. 383 (6): 1009–13. doi:10.1007/s00216-005-0069-7. PMID 16228199.Jump up^ "Merck's Manual 1899" (First ed.). Retrieved 16 June 2013.Jump up^ FDA. "Thimerosal in Vaccines". Retrieved 25 October 2006.Jump up^ Parker SK; Schwartz B; Todd J; Pickering LK (2004). "Thimerosal-containing vaccines and autistic spectrum disorder: a critical review of published original data". Pediatrics. 114 (3): 793–804. doi:10.1542/peds.2004-0434. PMID 15342856.Erratum (2005). Pediatrics 115 (1): 200. doi:10.1542/peds.2004-2402 PMID 15630018.Jump up^ "Thimerosal in vaccines". Center for Biologics Evaluation and Research, U.S. Food and Drug Administration. 6 September 2007. Retrieved 1 October 2007.Jump up^ Liu J; Shi JZ; Yu LM; Goyer RA; Waalkes MP (2008). "Mercury in traditional medicines: is cinnabar toxicologically similar to common mercurials?". Exp. Biol. Med. (Maywood). 233 (7): 810–7. doi:10.3181/0712-MR-336. PMC 2755212 . PMID 18445765.Jump up^ "Two States Pass First-time Bans on Mercury Blood Pressure Devices". Health Care Without Harm. 2 June 2003. Retrieved 1 May 2007.Jump up^ "Title 21—Food and Drugs Chapter I—Food and Drug Administration Department of Health and Human Services Subchapter D—Drugs for Human Use Code of federal regulations". United States Food and Drug Administration. Retrieved 1 May 2007.Jump up^ The CRB Commodity Yearbook (annual). 2000. p. 173. ISSN 1076-2906.^ Jump up to:a b Leopold, B. R. (2002). "Chapter 3: Manufacturing Processes Involving Mercury. Use and Release of Mercury in the United States." (PDF). National Risk Management Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio. Archived from the original(PDF) on 21 June 2007. Retrieved 1 May 2007.Jump up^ "Chlorine Online Diagram of mercury cell process". Euro Chlor. Archived from the original on 2 September 2006. Retrieved 15 September 2006.Jump up^ "Mercury Reduction Act of 2003". United States. Congress. Senate. Committee on Environment and Public Works. Retrieved 6 June 2009.Jump up^ "Liquid-mirror telescope set to give stargazing a new spin". Govert Schilling. 14 March 2003. Archived from the original on 18 August 2003. Retrieved 11 October 2008.Jump up^ Gibson, B. K. (1991). "Liquid Mirror Telescopes: History". Journal of the Royal Astronomical Society of Canada. 85: 158. Bibcode:1991JRASC..85..158G.Jump up^ "Laval University Liquid mirrors and adaptive optics group". Retrieved 24 June 2011.Jump up^ Brans, Y W; Hay W W (1995). Physiological monitoring and instrument diagnosis in perinatal and neonatal medicine. CUP Archive. p. 175. ISBN 0-521-41951-4.Jump up^ Zoski, Cynthia G. (7 February 2007). Handbook of Electrochemistry. Elsevier Science. ISBN 0-444-51958-0.Jump up^ Kissinger, Peter; Heineman, William R. (23 January 1996). Laboratory Techniques in Electroanalytical Chemistry, Second Edition, Revised and Expanded (2nd ed.). CRC. ISBN 0-8247-9445-1.Jump up^ Hopkinson, G. R.; Goodman, T. M.; Prince, S. R. (2004). A guide to the use and calibration of detector array equipment. SPIE Press. p. 125. ISBN 0-8194-5532-6.Jump up^ Howatson A H (1965). "Chapter 8". An Introduction to Gas Discharges. Oxford: Pergamon Press. ISBN 0-08-020575-5.Jump up^ Milo G E; Casto B C (1990). Transformation of human diploid fibroblasts. CRC Press. p. 104. ISBN 0-8493-4956-7.Jump up^ Shionoya, S. (1999). Phosphor handbook. CRC Press. p. 363. ISBN 0-8493-7560-6.Jump up^ "Mercury in your eye?". CIDPUSA. 16 February 2008. Retrieved 20 December 2009.Jump up^ McKelvey W; Jeffery N; Clark N; Kass D; Parsons PJ. 2010 (2011). "Population-Based Inorganic Mercury Biomonitoring and the Identification of Skin Care Products as a Source of Exposure in New York City". Environ Health Perspect. 119 (2): 203–9. doi:10.1289/ehp.1002396. PMC 3040607 . PMID 20923743.Jump up^ Healy, Paul F.; Blainey, Marc G. (2011). "Ancient Maya Mosaic Mirrors: Function, Symbolism, And Meaning". Ancient Mesoamerica. Cambridge University Press. 22 (2): 229–244 (241). doi:10.1017/S0956536111000241.Jump up^ Lew K (2008). Mercury. The Rosen Publishing Group. p. 10. ISBN 1-4042-1780-0.Jump up^ Pearson L F (2003). Lighthouses. Osprey Publishing. p. 29. ISBN 0-7478-0556-3.Jump up^ Ramanathan E. AIEEE Chemistry. Sura Books. p. 251. ISBN 81-7254-293-3.Jump up^ Shelton, C (2004). Electrical Installations. Nelson Thornes. p. 260. ISBN 0-7487-7979-5.Jump up^ Popular Science. 118. Bonnier Corporation. 1931. p. 40. ISSN 0161-7370.Jump up^ Mueller, Grover C. (September 1929). Cheaper Power from Quicksilver. Popular Science.Jump up^ Mercury as a Working Fluid. Museum of Retro Technology. 13 November 2008.Jump up^ Collier (1987). Introduction to Nuclear Power. Taylor & Francis. p. 64. ISBN 1-56032-682-4.Jump up^ "Glenn Contributions to Deep Space 1". NASA. Retrieved 7 July 2009.Jump up^ "Electric space propulsion". Retrieved 7 July 2009.Jump up^ "IMERC Fact Sheet: Mercury Use in Batteries". Northeast Waste Management Officials' Association. January 2010. Retrieved 20 June 2013.Jump up^ Gray, T. (22 September 2004). "The Amazing Rusting Aluminum". Popular Science. Retrieved 7 July 2009.Jump up^ Dufault, Renee; Leblanc, Blaise; Schnoll, Roseanne; Cornett, Charles; Schweitzer, Laura; Wallinga, David; Hightower, Jane; Patrick, Lyn; Lukiw, Walter J. (2009). "Mercury from Chlor-alkali plants". Environmental Health. 8: 2. doi:10.1186/1476-069X-8-2. PMC 2637263 . PMID 19171026.Jump up^ Francis, G. W. (1849). Chemical Experiments. D. Francis. p. 62.Jump up^ Castles, WT; Kimball, VF (2005). Firearms and Their Use. Kessinger Publishing. p. 104. ISBN 978-1-4179-8957-7.Jump up^ Lee, J.D. (1999). Concise Inorganic Chemistry. Wiley-Blackwell. ISBN 978-0-632-05293-6.Jump up^ Waldron, HA (1983). "Did the Mad Hatter have mercury poisoning?". Br Med J (Clin Res Ed). 287 (6409): 1961. doi:10.1136/bmj.287.6409.1961. PMC 1550196 . PMID 6418283.Jump up^ Alpers, C. N.; Hunerlach, M. P.; May, J. Y.; Hothem, R. L. "Mercury Contamination from Historical Gold Mining in California". U.S. Geological Survey. Retrieved 26 February 2008.Jump up^ "Mercury amalgamation". Corrosion Doctors. Retrieved 7 July 2009.Jump up^ Pimple, K.D. Pedroni; J.A. Berdon, V. (9 July 2002). "Syphilis in history". Poynter Center for the Study of Ethics and American Institutions at Indiana University-Bloomington. Archived from the original on 16 February 2005. Retrieved 17 April 2005.Jump up^ Mayell, H. (17 July 2007). "Did Mercury in "Little Blue Pills" Make Abraham Lincoln Erratic?". National Geographic News. Retrieved 15 June 2008.Jump up^ "What happened to Mercurochrome?". 23 July 2004. Retrieved 7 July 2009.Jump up^ "Mercury: Spills, Disposal and Site Cleanup". Environmental Protection Agency. Retrieved 11 August 2007.Jump up^ "Glacial Ice Cores Reveal A Record of Natural and Anthropogenic Atmospheric Mercury Deposition for the Last 270 Years". United States Geological Survey (USGS). Retrieved 1 May 2007.^ Jump up to:a b c Pacyna E G; Pacyna J M; Steenhuisen F; Wilson S (2006). "Global anthropogenic mercury emission inventory for 2000". Atmos Environ. 40 (22): 4048. Bibcode:2006AtmEn..40.4048P. doi:10.1016/j.atmosenv.2006.03.041.Jump up^ "What is EPA doing about mercury air emissions?". United States Environmental Protection Agency (EPA). Retrieved 1 May 2007.Jump up^ Solnit, R. (September–October 2006). "Winged Mercury and the Golden Calf". Orion Magazine. Retrieved 3 December 2007.Jump up^ Maprani, Antu C.; Al, Tom A.; MacQuarrie, Kerry T.; Dalziel, John A.; Shaw, Sean A.; Yeats, Phillip A. (2005). "Determination of Mercury Evasion in a Contaminated Headwater Stream". Environmental Science & Technology. 39 (6): 1679. Bibcode:2005EnST...39.1679M. doi:10.1021/es048962j.Jump up^ "Indoor Air Mercury" (PDF). Northeast Waste Management Officials' Association (NEWMOA). May 2003. Retrieved 7 July 2009.Jump up^ "Mercury-containing Products". United States Environmental Protection Agency (EPA). Retrieved 1 May 2007.Jump up^ IMERC Fact Sheet – Mercury Use in Thermostats January 2010Jump up^ "Introduction". United States Department of Energy.Jump up^ "Minamata Disease The History and Measures". Ministry of the Environment, Government of Japan. Retrieved 7 July 2009.Jump up^ Dennis Normile (27 September 2013). "In Minamata, Mercury Still Divides". Science. 341: 1446. Bibcode:2013Sci...341.1446N. doi:10.1126/science.341.6153.1446. PMID 24072902.Jump up^ Ngim, CH; Foo, SC; Boey, K.W.; Keyaratnam, J (1992). "Chronic neurobehavioral effects of elemental mercury in dentists". British Journal of Industrial Medicine. 49 (11): 782–90. doi:10.1136/oem.49.11.782. PMC 1039326 . PMID 1463679.Jump up^ Liang, Y. X.; Sun, R. K.; Sun, Y.; Chen, Z. Q.; Li, L. H. (1993). "Psychological effects of low exposure to mercury vapor: Application of computer-administered neurobehavioral evaluation system". Environmental Research. 60 (2): 320–7. Bibcode:1993ER.....60..320L. doi:10.1006/enrs.1993.1040. PMID 8472661.Jump up^ McFarland, RB & Reigel, H (1978). "Chronic Mercury Poisoning from a Single Brief Exposure". J. Occup. Med. 20 (8): 532. doi:10.1097/00043764-197808000-00003.Jump up^ Mercury, Environmental Health Criteria monograph No. 001, Geneva: World Health Organization, 1976, ISBN 92-4-154061-3Jump up^ Inorganic mercury, Environmental Health Criteria monograph No. 118, Geneva: World Health Organization, 1991, ISBN 92-4-157118-7Jump up^ Bluhm, RE; et al. (1992). "Elemental Mercury Vapour Toxicity, Treatment, and Prognosis After Acute, Intensive Exposure in Chloralkali Plant Workers. Part I: History, Neuropsychological Findings and Chelator effects.". Hum Exp Toxicol. 11 (3): 201–10. doi:10.1177/096032719201100308. PMID 1352115.Jump up^ Bluhm, Re; Bobbitt, Rg; Welch, Lw; Wood, Aj; Bonfiglio, Jf; Sarzen, C; Heath, Aj; Branch, Ra (1992). "Elemental mercury vapour toxicity, treatment, and prognosis after acute, intensive exposure in chloralkali plant workers. Part I: History, neuropsychological findings and chelator effects.". Human & Experimental Toxicology. 11 (3): 201–10. doi:10.1177/096032719201100308. PMID 1352115.Jump up^ Cocoros, G.; Cahn, P. H.; Siler, W. (1973). "Mercury concentrations in fish, plankton and water from three Western Atlantic estuaries" (PDF). Journal of Fish Biology. 5 (6): 641–647. doi:10.1111/j.1095-8649.1973.tb04500.x.Jump up^ "Minamata Convention Agreed by Nations". United Nations Environment Program. Retrieved 19 January 2013.Jump up^ Section, United Nations News Service (2013-01-19). "UN News — Governments at UN forum agree on legally-binding treaty to curb mercury pollution". UN News Service Section. Retrieved 2016-11-22.Jump up^ "Mercury: Laws and regulations". United States Environmental Protection Agency. 16 April 2008. Retrieved 30 May 2008.Jump up^ "Reductions in Mercury Emissions". International Joint Commission on the Great Lakes.Jump up^ "Clean Air Mercury Rule". United States Environmental Protection Agency (EPA). Retrieved 1 May 2007.Jump up^ "State of New Jersey et al., Petitioners vs. Environmental Protection Agency (Case No. 05-1097)" (PDF). United States Court of Appeals for the District of Columbia Circuit. Argued 6 December 2007, Decided 8 February 2008. Retrieved 30 May 2008.Jump up^ Mark S. Castro, John Sherwell, Effectiveness of Emission Controls to Reduce the Atmospheric Concentrations of Mercury. In: Environmental Science & Technology 49, 2015, 14000−14007, doi:10.1021/acs.est.5b03576.Jump up^ "Oldest, dirtiest power plants told to clean up". Boston Globe. 22 December 2011. Retrieved 2 January 2012.Jump up^ Howard Berkes (10 November 2011). "EPA Regulations Give Kilns Permission To Pollute". NPR. Retrieved 2 January 2012.Jump up^ "Directive 2002/95/EC on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment". 27 January 2003. Article 4 Paragraph 1. e.g. "Member States shall ensure that, from July 1, 2006, new electrical and electronic equipment put on the market does not contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE)."Jump up^ "Mercury compounds in European Union:". EIA Track. 2007. Retrieved 30 May 2008.Jump up^ Jones H. (10 July 2007). "EU bans mercury in barometers, thermometers". Reuters. Retrieved 30 May 2008.Jump up^ "Norway to ban mercury". EU Business. 21 December 2007. Archived from the original on 21 January 2008. Retrieved 30 May 2008.Jump up^ Berg, T; Fjeld, E; Steinnes, E (2006). "Atmospheric mercury in Norway: contributions from different sources". The Science of the total environment. 368 (1): 3–9. doi:10.1016/j.scitotenv.2005.09.059. PMID 16310836.^ Jump up to:a b Edlich, Richard F.; Rhoads, Samantha K.; Cantrell, Holly S.; Azavedo, Sabrina M. and Newkirk, Anthony T. Banning Mercury Amalgam. US FDAJump up^ "Sweden to ban mercury — The Local". 14 January 2009. Archived from the original on 28 August 2016. Retrieved 2016-11-22.Jump up^ "Sweden may be forced to lift ban on mercury — The Local". 21 April 2012. Archived from the original on 28 August 2016. Retrieved 2016-11-22.Further readingAndrew Scott Johnston, Mercury and the Making of California: Mining, Landscape, and Race, 1840–1890. Boulder, CO: University Press of Colorado, 2013.External linksWikimedia Commons has media related to Mercury (element).Wikiquote has quotations related to: Mercury (element)Look up mercury in Wiktionary, the free dictionary.Chemistry in its element podcast (MP3) from the Royal Society of Chemistry's Chemistry World: MercuryMercury at The Periodic Table of Videos (University of Nottingham)Centers for Disease Control and Prevention – Mercury TopicEPA fish consumption guidelinesHg 80 MercuryMaterial Safety Data Sheet – MercuryStopping Pollution: Mercury – OceanaNatural Resources Defense Council (NRDC): Mercury Contamination in Fish guide – NRDCNLM Hazardous Substances Databank – MercuryBBC – Earth News – Mercury 'turns' wetland birds such as ibises homosexualChanging Patterns in the Use, Recycling, and Material Substitution of Mercury in the United States United States Geological SurveyThermodynamical data on liquid mercury."Mercury (element)". Encyclopædia Britannica (11th ed.). 1911.[hide]vtePeriodic table(Large cells)1234567891011121314151617181HHe2LiBeBCNOFNe3NaMgAlSiPSClAr4KCaScTiVCrMnFeCoNiCuZnGaGeAsSeBrKr5RbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIXe6CsBaLaCePrNdPmSmEuGdTbDyHoErTmYbLuHfTaWReOsIrPtAuHgTlPbBiPoAtRn7FrRaAcThPaUNpPuAmCmBkCfEsFmMdNoLrRfDbSgBhHsMtDsRgCnNhFlMcLvTsOgAlkali metalAlkaline earth metalLan­thanideActinideTransition metalPost-​transition metalMetalloidPolyatomic nonmetalDiatomic nonmetalNoble gasUnknownchemicalproperties[show]vteMercury compoundsAuthority controlWorldCat IdentitiesVIAF: 6418653LCCN: sh85083794GND: 4127830-6NDL: 00571550Categories:Mercury (element)Chemical elementsTransition metalsOccupational safety and healthEndocrine disruptorsCoolantsNuclear reactor coolantsNeurotoxinsNative element mineralsNavigation menuNot logged inTalkContributionsCreate accountLog inArticleTalkReadView sourceView historySearchMain pageContentsFeatured contentCurrent eventsRandom articleDonate to WikipediaWikipedia storeInteractionHelpAbout WikipediaCommunity portalRecent changesContact pageToolsWhat links hereRelated changesUpload fileSpecial pagesPermanent linkPage informationWikidata itemCite this pagePrint/exportCreate a bookDownload as PDFPrintable versionIn other projectsWikimedia CommonsWikiquoteLanguagesAfrikaansአማርኛالعربيةAragonésArmãneashtiAsturianuAvañe'ẽAzərbaycancaবাংলাBân-lâm-gúБеларускаяБеларуская (тарашкевіца)‎भोजपुरीBikol CentralБългарскиབོད་ཡིགBosanskiBrezhonegCatalàЧӑвашлаČeštinaCorsuCymraegDanskDeutschDiné bizaadEestiΕλληνικάEmiliàn e rumagnòlЭрзяньEspañolEsperantoEuskaraفارسیFiji HindiFøroysktFrançaisFurlanGaeilgeGaelgGàidhligGalegoGĩkũyũગુજરાતી客家語/Hak-kâ-ngîХальмг한국어Հայերենहिन्दीHrvatskiIdoBahasa IndonesiaInterlinguaИронIsiXhosaÍslenskaItalianoעבריתಕನ್ನಡKapampanganქართულიҚазақшаKiswahiliКомиKreyòl ayisyenKurdîКыргызчаКырык марыЛаккуLatinaLatviešuLëtzebuergeschLietuviųLigureLimburgsLivvinkarjalaLa .lojban.LumbaartMagyarМакедонскиമലയാളംMāoriमराठीمصرىمازِرونیBahasa MelayuMìng-dĕ̤ng-ngṳ̄МонголNāhuatlNederlandsनेपाल भाषा日本語Norsk bokmålNorsk nynorskOccitanОлык марийଓଡ଼ିଆOʻzbekcha/ўзбекчаਪੰਜਾਬੀپنجابیپښتوПерем КомиPiemontèisPlattdüütschPolskiPortuguêsRomânăRuna SimiРусскийसंस्कृतम्ScotsSeelterskShqipSicilianuසිංහලSimple EnglishSlovenčinaSlovenščinaŚlůnskiSoomaaligaکوردیی ناوەندیСрпски / srpskiSrpskohrvatski / српскохрватскиBasa SundaSuomiSvenskaTagalogதமிழ்Татарча/tatarçaไทยTürkçeУкраїнськаاردوVahcuenghVepsän kel’Tiếng ViệtWalon文言WinarayייִדישYorùbá粵語中文Edit linksThis page was last edited on 29 April 2017, at 13:53.Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.Privacy policyAbout WikipediaDisclaimersContact WikipediaDevelopersCookie statementMobile view

Fatty Acids: Branched-ChainBranched-chain fatty acids are common constituents of the lipids of bacteria and animals, although they are rarely found other than as surface lipids of higher plants. Normally, the fatty acyl chain is saturated and the branch is a methyl-group, but unsaturated branched-chain fatty acids are found in marine animals, and branches other than methyl may be present in microbial lipids. The most common branched chain fatty acids are mono-methyl-branched, but di- and poly-methyl-branched fatty acids are also known and the mycolic acids especially are highly complex. Their main function in membranes may be to increase the fluidity and lower the phase transition temperature of the lipid components as an alternative to unsaturated fatty acids. As they have mainly saturated aliphatic chains, branched-chain fatty acids are not vulnerable to attack by activated oxygen, and this may be an explanation for their occurrence on surfaces exposed to oxygen flux, such as skin and tear films. They are also claimed to inhibit the growth of cancer cells in vitro. The following discussion is not intended to be comprehensive.Saturated iso- and anteiso-Methyl-Branched Fatty Acidsiso-Methyl branched fatty acids have the branch point on the penultimate carbon (one from the end or (ω-1)), while anteiso-methyl-branched fatty acids have the branch point on the ante-penultimate carbon atom (two from the end or (ω-2)) as illustrated. In the latter, the methyl group has the (S)-configuration in general, reflecting its biosynthetic origin, but a small proportion of the R-enantiomer has been detected in soil bacteria, for example. The common range of fatty acids of this kind with a single branch point only in a saturated chain are discussed in this section.Fatty acids with structures of this type and with 10 to more than 30 carbons in the acyl chain are found in nature, but those most often encountered have 14 to 18 carbons in the chain (not counting the additional carbon in the methyl group). They are common constituents of bacteria but are rarely found in other microorganisms. Via the food chain, they can be found in animal tissues, especially those of marine animals and ruminants. However, they can also be synthesised in animal tissues per se. In bacteria, their content and composition can often be used as taxonomic markers, and in the genus Bacillus, for example, some species have fatty acids with the iso-structure only, while others have the anteiso-structure.These fatty acids are produced biosynthetically via the conventional mechanisms for the synthesis of saturated fatty acids in bacteria (FAS II - see the appropriate web page), except that the nature of the primer molecule differs. Thus, instead of acetyl-coA, 2-methylpropanyl-CoA (derived from the amino acid valine) is the primer for the biosynthesis of iso-branched fatty acids with an even number of carbon atoms (odd-numbered chain), while 3-methylbutyryl-CoA (derived from leucine) is the primer for iso-fatty acids with an odd number of carbon atoms (even-numbered chain). 2-Methyl-butyryl-CoA (derived from isoleucine) is the primer for anteiso-fatty acids to produce fatty acids with an odd number of carbon atoms (even-numbered chain). The first step in the generation of the fatty acid primers is the conversion of each branched-chain amino acid to its corresponding α-keto acid by mitochondrial branched-chain aminotransferase, and this is followed by reaction with the rate-limiting enzyme, branched-chain α-ketoacid dehydrogenase, which produces each of the primer-CoA esters. Whether the FAS II can utilize such branched precursors depends upon the specificity of the malonyl-CoA condensation enzyme II (FABH). For example that in Escherichia coli cannot use them, but Bacillus subtilis has two FABH enzymes, which both prefer branched-chain substrates. Dolphins synthesise branched-chain fatty acids from leucine whereas beaked whales use valine as the precursor, but enzymes that can elongate isovaleric acid appear to be absent or limited in their activity.It is more common to find iso-methyl fatty acids with an even number of carbons in total, although the chain-length is odd-numbered, while the opposite is true for the anteiso-forms. Note: this sometimes leads to confusion in the informal nomenclatures that may be used in scientific publications. For example, 13-methyl-tetradecanoate acid is sometimes abbreviated to iso-methyl-14:0 and sometimes iso-methyl-15:0; I prefer the former as it better reflects the systematic name. Because of the alternative route for iso-methyl formation and alpha-oxidation processes, odd-numbered iso-methyl acids and even-numbered anteiso-methyl acids are also found in tissues.In animal tissues, the biosynthesis of these fatty acids de novo is normally a very minor process and is believed to involve the same mechanism as above. However, it can occur at a significant rate in some instances. For example, lanolin, the waxy material produced as a protective coating for the fleece of sheep, contains up to 45% of iso- and anteiso-branched fatty acids from C10to C34in chain-length (see the web page on waxes). One anteiso-branched fatty acid, 18-methyl-eicosanoic acid, constitutes up 60% of the total fatty acids esterified directly to wool via thiol ester bonds, and it comprises 40% or more of the same lipid in all mammalian hairs examined to date. A significant proportion of the lipids secreted by the meibomian glands adjacent to the eye consist of iso/anteiso-methyl-branched fatty acids. Triacylglycerols and wax esters containing isovaleric(3-methylbutyric) acid and other branched-chain fatty acids are important constituents of the blubber and melon (echo location) oils of the toothed whales and dolphins, and an alkyldiacylglycerol containing this acid occurs in rabbit harderian gland.However, in most mammalian tissues, branched-chain fatty acids of this type rarely make up more that 1-2% of the total, and are probably derived mainly from bacteria in the intestines or from consumption of such fatty acids in dairy products or meat from ruminant animals. Similarly fish oils usually contain 1-2% iso- and anteiso-fatty acids of chain-length C14to C18, which are presumed to be derived from the marine food chain.The free-living nematode Caenorhabditis eleganssynthesises iso-methyl-tetradecanoic and hexadecanoic acids de novo and has been shown to be absolutely dependent on these for its growth and development. Acyl-CoA synthetases guide the incorporation of branched-chain acids into specific phospholipids and thus regulate the phospholipid composition in the zygote. Disruption of the biosynthesis of these fatty acids, for example by inhibiting the branched-chain α-ketoacid dehydrogenase, leads to early embryonic fatality, but supplementation with long-chain methyl-branched fatty acids corrects the problem.In higher plants, branched-chain components are only rarely reported from the seeds or green tissues, but 14-methylhexadecanoic occurs at a level of 0.5 to 1% in seed oils from the family Pinaceae, where it appears to be a useful taxonomic marker, and anteiso-methyl-branched fatty acids have been characterized from the main tissues (non-wax) of Brussels sprouts.iso-/anteiso-Methyl-branched fatty acids are major components of plant surface waxes, however.Neo fatty acids, which can be considered as having a terminal tertiary butyl group or with two iso-methyl groups, have been found in certain microorganisms, algae, plants and marine invertebrates. For example, 13,13-dimethyltetradecanoic acid or ‘neopalmitic acid’ illustrated is a minor component of bark and resins from conifers and other plants, and it has been found in the shell, chitin and chitosan of a species of crab.Saturated Mid-Chain Methyl-Branched Fatty AcidsBacterial fatty acids: 10-R-Methyloctadecanoic acid or tuberculostearic acid is a major component of the lipids of the tubercle bacillus and related bacterial species. Indeed its presence in bacterial cultures and sputum from patients is used in the diagnosis of tuberculosis. It is also found in Corynebacterium and some other bacterial species.A number of fatty acids with a single methyl branch of this type have been isolated from other bacterial species. For example, 10-methylhexadecanoic and 11-methyloctadecanoic acids are relatively common microbial constituents, and 12-methylhexadecanoic acid and 14-methyloctadecanoic acid are major components of the halotolerant bacterium Rubrobacter radiotolerans. The latter occurs in the aquatic bacterium Rhodococcus equi also. 6- and 9-Methyltetradecanoic acids are found in lichenized fungi. Mycobacterium phlei contains a range of methyl-branched fatty acids, including 8- and 10-methylhexadecanoate, 9-methylheptadecanoate, 11-methylnonadecanoate, 12-methyleicosanoate, 14-methyldocosanoate and 16-methyltetracosanoate. In mixed microbial populations such as those isolated from soil or other environmental samples, many different branched-chain fatty acids of this type may be found.Sponges and some other marine organisms contain methyl-branched fatty acids, but these are derived from microorganisms in their diet or that live in symbiosis with them. For example, in addition to a number of iso- and anteiso-methyl-branched fatty acids, 10-methyl-16:0, 11-methyl-18:0, 14-methyl-20:0, 18-methyl-24:0 and 20-methyl-26:0 were found in the lipids of the sponge Verongia aerophoba.Biosynthesis of branched-chain fatty acids of this type involves methylation at the double bond of a monoenoic acid such as oleic or cis-vaccenic acid esterified as a component of a phospholipid, with S-adenosylmethionine as the methyl donor. The resulting (R)-10-methylene-octadecanoyl residue is reduced to the 10-methyl compound with NADPH as the cofactor; the intermediate 10-methylene-octadecanoic acid has been isolated from a Corynebacterium. A related mechanism is used for biosynthesis of cyclopropane fatty acids in bacteria.Animal sources: Ruminant fats also contain high proportions of branched-chain components, especially when they are fed carbohydrate-rich diets, when up to 9% of the subcutaneous fat can comprise such fatty acids. Relatively high proportions of propionic acid (as opposed to acetic and butyric) are produced by the rumen microorganisms under this regime, and this metabolite is in turn converted to methylmalonyl-CoA, which is incorporated into fatty acids by the fatty acid synthase (FAS I). A consequence of this mechanism is that the methyl groups are all in the even-numbered positions, and are distributed randomly in fatty acids of varying chain-lengths. In fact more than 120 different mono-, di- and tri-methyl fatty acids (and some ethyl-branched components) have been identified in ruminant fats.Some such methyl-branched fatty acids occur in a few disparate tissues in the animal kingdom. Perhaps the best known is the uropygial (preen) gland of birds that secretes a waxy material that serves to waterproof the feathers. While the precise composition of this varies from species to species, all are characterized by high concentrations of branched-chain fatty acids (and alcohols). Usually the branch is a methyl group, but ethyl and propyl branches are also known. The positions of these and the chain-lengths of the various components cover a wide range, but for the monomethyl fatty acids, the branch-points are most often in positions 2 to 6. Di-, tri- and tetramethyl-branched fatty acids are also present. A common pattern is to find series such as 2,4-, 2,6-, 2,8- and 4,6-dimethyl, and so forth, with 2,4,6-, 2,4,8- and 2,6,8-trimethyl, and 2,4,6,8-tetramethyl fatty acids. In some species, these can comprise 90% of the total fatty acids. However, the preen gland of the barn owl contains 3-methyl- and 3,5-, 3,7-, 3,9-, 3,11-, 3,13-, and 3,15-dimethyl-branched fatty acids. As an example, the composition of the fatty acids in the uropygial gland of the fulmar is listed in Table 1. Much remains to be learned of the mechanism of biosynthesis of these fatty acids, but again it appears that a high proportion at least is produced via methylmalonyl-CoA instead of malonyl-CoA for chain-elongation and to insert the methyl group.Table 1. Branched-chain components in the preen gland of the fulmar (wt% of the total).PositionChain-lengthAmount (%)2-C80.43-C7to C1253.34-C7to C1222.66-C10to C124.02,4-/2,6-C8to C106.53,7-C9to C118.34,6-/4,8-C100.4Jacob, J. and Zeman, A. Z. Naturforsch., 26b, 33 (1971).A further interesting example is Vernix caseosa, the waxy skin secretion that covers newborn babies. In addition to a high proportion of iso- and anteiso-methyl-branched fatty aids, this contains approximately 10% of components from C11to C18in chain-length with methyl groups in the even-numbered positions from 2 to 12, which are once more presumably synthesised using methylmalonate as a substrate. These fatty acids are also found in the intestines of new-born, where they arise from lipid-laden vernix caseosa particles suspended in amniotic fluid; there is a suggestion that they may inhibit microbial attack.Multi-branched from bacteria: Non-isoprenoid dimethyl-branched fatty acids are frequently reported from bacteria. For example, 4,9-dimethyl-10:0, 4,10- and 4,11-dimethyl-12:0, and 4,13-dimethyl-14:0 acids, with 2,13- and 2,12-dimethyl-14:0 acids were identified in a halophilic Bacillus sp. Multi-branched fatty acids with the methyl branches in positions 2-, 4-, 6- and 8- are present in certain Mycobacteria. Dimethyl fatty acids are occasionally reported from sponges, where they are presumed to be derived from bacteria in the food chain or that are symbiotic, e.g. 9,13- and 10,13-dimethyl-14:0, 8,10-dimethyl-16:0 and 3,13-dimethyl-14:0.Dimethyl, dibasic acids such as the 'diabolic acids', have been reported from Butyrivibrio spp., and related fatty acids are found in many species from the genus Acidobacteria. They are apparently formed biosynthetically by a tail to tail joining of two conventional fatty acids. Each of the carboxyl groups can link to a glycerol moiety as part of a highly complex lipid that can span a membrane bilayer. Similar fatty acids occur in some plant waxes.Diabolic acid per se is 15,16-dimethyltriacontanedioic acid, while isodiabolic acid is 13,14-dimethyloctacosanedioic acid, and 5,13,14-trimethyloctacosanedioic acid is also known. In Acidobacteria, ether-linked analogues are found in the complex membrane-spanning lipids.Isoprenoid Fatty AcidsA number of isoprenoid fatty acids that are derived from the metabolism of phytol (3,7,11,15-tetramethylhexadec-trans-2-en-1-ol), the aliphatic alcohol moiety of chlorophyll, occur naturally in animal tissues. These range from 2,6-dimethylheptanoic to 5,9,13,17-tetramethyloctadecanoic acids, but those encountered most often are 3,7,11,15-tetramethylhexadecanoic (phytanic) and 2,6,10,14-tetramethylpentadecanoic (pristanic) acids. 4,8,12-Trimethyltridecanoic acid is especially common in fish and other marine organisms. Phytanic acid occurs in tissues as a racemic mixture of (3R,7R,11R,15)- and (3S,7R,11R,15)-tetramethylhexadecanoic acids.Normally, these fatty acids occur at low levels only in tissues, with the concentrations being highest in herbivores. For example, phytanic acid is found at levels of up to 1% normally in milk fat and adipose tissue from cows. However, much higher concentrations can occur on occasion. For example, up to 20% of the fatty acids in the triacylglycerols of bovine plasma can consist of this acid, because the methyl-branch in position 3 of the chain inhibits the action of the enzyme lipoprotein lipase that clears triacylglycerols from plasma.Dietary chlorophyll cannot be hydrolysed to phytol in the digestive system of humans, but rumen microorganism can accomplish this. In the tissues of ruminant animals, phytanic acid is formed by oxidation of phytol first to phytenal and then to phytenic acid (with a double bond in position 2 and only encountered in tissues under artificial feeding conditions), followed by reduction. Most of the phytanic acid in the tissues of humans is ingested via meat and dairy products, and shorter-chain isoprenoid fatty acids are formed from this by sequential α- and/or β-oxidation reactions. Presumably, phytanic acid is formed in an analogous manner in fish and can thence enter the human food chain also.Because of the presence of the 3-methyl group, degradation of phytanic acid by β-oxidation cannot be initiated in animal tissues. Rather, phytanic acid is oxidized first by α-oxidation in peroxisomes, yielding pristanic acid, which can then be subjected to three cycles of β-oxidation with 4,8-dimethylnonanoyl-CoA as the end product; this is transported to mitochondria where full oxidation takes place. Some omega-oxidation occurs also with 3-methyladipic acid as an end-product. In humans, several inborn metabolic errors in the degradation of phytanic and pristanic acids have been described that lead to an accumulation of these acids in tissues and body fluids. There are various clinical expressions of these disorders, some of which can be fatal, the best known of which is Refsum’s disease, a rare human genetic syndrome. In this disease, defects in one or other steps in the α-oxidation system, but mainly in the enzyme phytanoyl-CoA 2-hydroxylase, lead to the accumulation of phytanic acid in tissues and to clinical symptoms.In contrast, there are suggestions that phytanic and pristanic acids may an number of beneficial influences towards heath that include protective effects against the metabolic syndrome, induction of the differentiation of brown adipocytes, and inhibition of breast, colon and other cancers. They are signalling molecules that function by regulating the expression of those genes that affect the catabolism of lipids in animal tissues. By binding to a liver-type fatty acid binding protein, they are transported to the nucleus where they exert their effects by binding to the α-subtype of the peroxisome proliferator-activated receptors (PPAR), which induces the transcription of enzymes involved in fatty acid degradation by β- and ω-oxidation. In a sense, they are regulators of their own degradation. Also, phytanic acid functions also as a regulator of aspects of glucose and retinoic acid metabolism.Similarly, retinoic acid, an isoprenoid acid derived from vitamin A, is an important regulator of genes involved in cell growth and differentiation via distinct transport proteins and nuclear receptors, but it has its own web page. In contrast to phytanic acid, it is not found esterified to mainstream lipids in tissues.Unsaturated Methyl-Branched Fatty AcidsMonounsaturated methyl branched-chain fatty acids have been detected in bacteria and marine animals. Often, the branch is in the iso/anteiso-position, but it can also be more central in the aliphatic chain. For example, one of the first acids of this type to be described was 7-methyl-7-hexadecenoic acid from lipids of the ocean sunfish (Mola mola), while 7-methyl-6- and 7-methyl-8-hexadecenoic acids were later found in sponges.Similar fatty acids with iso-/anteiso-methyl groups to have been detected in related marine organisms include 13-methyltetradec-4-enoic, 14-methylhexadec-6-enoic, 14-methylpentadec-6-enoic and 17-methyloctadec-8-enoic acids, and many others. It is possible that the primary origin of these fatty acids is in bacteria, as these can contain many comparable fatty acids, for example in Bacillus cereus, B. megaterium and Desulfovibrio desulfuricans.Many different demospongic acids, i.e. with bis-methylene-interrupted double bonds (usually in the 5,9-positions), have been found with iso- and anteiso-methyl branches (see our web page dealing withdemospongic acids). In addition, several related fatty acids have been described with the methyl group in more central positions, e.g. 17-methyl-5,9-24:2, 21-methyl-5,9-26:2 and 22-methyl-5,9-28:2. Unusual multibranched polyunsaturated and very-long-chain fatty acids have been located in slime moulds and freshwater sponges from Israel, including (2E,4E,7S,8E10E12E14S)-7,9,13,17-tetramethyl-7,14-dihydroxy-2,4,8,10,12,16-octadecahexaenoic acid from seven different species of myxomycetes.Branched-chain fatty acids are not common in plants, but small amounts of 16-methyl-cis-9-octadecenoic and 16-methyl-cis-9,cis-12-octadecadienoic acids have been found in wood and seeds of certain Gymnosperm species.Mycolic and Related Fatty AcidsThe mycolic acids are major components of the cell walls of Mycobacteria and related species, including the genera Mycobacterium, Nocardia, Rhodococcusand Corynebacterium, where they are present mainly attached covalently to distinctive peptidoglycan-arabinogalactan complexes and to the trehalose lipids. They are β-hydroxy-α-alkyl branched structures of high molecular weight, and in Mycobacteria especially, these can have 60 to 90 carbons. The main unit is termed a "meromycolic chain", and depending on species, it can contain a variety of functional groups, including double bonds of both the cis- and trans-configurations (but when the latter, they also possess an adjacent methyl branch) and cyclopropane rings, which can also be of the cis- and trans-configurations. In addition, they can contain hydroxy, methoxy-, epoxy- and keto groups of distinct stereochemistry, which are also adjacent to a methyl branch normally. The 2R-,3R-stereochemistry of the substituents at positions 2 and 3 is conserved in all genera.The least polar mycolic acids, often termed alpha-mycolic acids, contain 74-80 carbon atoms and generally two double bonds (of the cis- or trans-configuration) or two cis-cyclopropyl groups located in the meromycolic chain; some may contain further double bonds, e.g. M. tuberculosis. The alpha'-mycolic acids have 60-62 carbon atoms and one cis double bond, with the alpha-branched unit commonly consisting of a C22to C26chain. Also, in M. tuberculosis, the oxygenated mycolic acids are 4-6 carbon atoms longer than the non-polar equivalents. The genus Segniliparus contains a distinctive series of mycolic acids, including the longest known (C42-C100) in which the alpha-mycolates lack the hydroxyl group in position 3. Some representative structures are illustrated below.The mycolic acids are key structural components of the membranes of mycobacteria, where they appear to confer distinctive properties, including a low permeability to hydrophobic compounds, resistance to dehydration, and the capacity to survive the hostile environment of the macrophage. The β-hydroxyl group is especially important in that it is believed to modulate both the phase transition temperature and the molecular packing within the membrane. The cell envelope of Mycobacterium tuberculosis, for example, has a distinctive lipid composition that is associated with its pathogenicity in tuberculosis infections. Thus, lipid mycolates are important as structural components of the cell wall, which protects the tubercle bacillus from the host’s immune system. Mycolic acids are major constituents of this layer as components of distinctive lipids and lipopolysaccharides, including an arabinogalactanmycolate covalently linked to the cell wall peptidoglycan via a phosphodiester bond, phenolphthiocerol and phthiocerol dimycocerosates, and trehalose esters, which include sulfatides and di- to penta-acyltrehaloses. In esterified form, they are believed to adopt a singular 'W' conformation. In addition, substantial amounts of free mycolic acids are present in the extracellular matrix of mycobacteria grown as biofilms, and indeed they are required for this type of growth.The cyclopropane rings in mycolic acids contribute to the structural integrity of the cell wall complex and are protective against oxidative stress. Experimentally induced changes to the structures of the mycolic acids lead to loss of virulence, and it is evident that oxygenated moieties are required for maximum activity.The two component parts of mycolic acids are each synthesised by different enzyme systems in the microorganisms before they are condensed to form a typical mycolic acid. In M. tuberculosis, a fatty acid synthetase I of the animal type has a bimodal product profile and provides C16to C20-acyl-CoAs to a fatty acid synthetase II system (FAS II, plant or prokaryotic type) for chain-elongation to produce the meromycolic chain (see our web pages on the biosynthesis of saturated fatty acids). The type 1 synthetase also produces C22-C26fatty acids for the alpha-branch-chain. The FAS-II systems consist of discrete monofunctional proteins, but mycobacterial FAS-II has the unique property of elongating standard-sized fatty-acid precursors (C16-C18) via iterative elongation cycles into the very-long-chain fatty acids, the meromycolic acids (C36-C72). There are four main catalytic steps centred on a mycobacterial acyl carrier protein, and three of these are catalysed by enzymes homologous to bacterial FAS-II components but the fourth (a hydratase) differs and is distinctive for Mycobacteria. Cis double bonds are introduced at two locations on a growing meroacid chain to yield three different forms of cis,cis-diunsaturated fatty acyl intermediates, which can then be converted to methyl, cyclopropane, methoxy- and keto-meroacids. Finally, the mature meroacids and a C26-S-acyl carrier protein enter into a Claisen-type condensation catalysed by a polyketide synthase to yield the mycolic acids. Transport of the mycolates to either the cell envelope or for attachment to arabinogalactans is believed to occur in the form of trehalose monomycolate.Recent findings that mycolic acids from M. tuberculosis and cholesterol interact with each other and bind to similar molecules are leading to a new understanding of host-pathogen interactions, which will hopefully lead to better control of the disease.Structural analysis of such complex fatty acids is much more difficult than with conventional fatty acids, and usually involves a battery of chromatographic and spectroscopic techniques, and especially mass spectrometry. One useful reaction involves pyrolysis to yield an alpha- or mero-fatty acid containing all the substituent groups and a mero-aldehyde, which can be analysed separately by mass spectrometry.Mycobacteric acids: Mycobacteria also contain multi-methyl-branched fatty acids (C14to C32), often with the methyl branches in positions 2, 4, 6 and 8, and sometimes with hydroxyl groups in position 3, together with long-chain (C36to C47) fatty acids termed 'mycobacteric' acids, which are structurally related to mycolic acids and contain cyclopropyl rings, double bonds (trans and cis) and/or oxygenated functions. Indeed, the latter are formed from the mycolic acids by a cleavage between carbons 3 and 4 by a Baeyer-Villiger-like reaction. Mycobacteric acids are present only in the triacylglycerol fraction, where they are esterified to one of the three hydroxyl groups of glycerol.Further multimethyl branched fatty acids found in Mycobacteria include mycoceranic (2,4,6-trimethyloctacosanoic), mycolipenic (2,4,6-trimethyl-trans-2-tetracosenoic) and mycocerosic (2,4,6,8-tetramethyl-dotriacontanoic (C32)) acids. The phthioceranic acids are hepta- or octamethyl fatty acids, some of which are also hydroxylated (hydroxyphthioceranic acid).

Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as productsChemical reactions are an integral part of technology, of culture, and indeed of . Burning fuels, smelting iron, making glass and pottery, brewing beer, and making wine and cheese are among many examples of activities incorporating chemical reactions that have been known and used for thousands of years. Chemical reactions abound in the geology of Earth, in the atmosphere and oceans, and in a vast array of complicated processes that occur in all living systems.Chemical reactions must be distinguished from physical changes. Physical changes include changes of state, such as ice melting to water and water evaporating to vapour. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same. No matter what its physical state, water (H2O) is the same compound, with each molecule composed of two atoms of hydrogen and one atom of oxygen. However, if water, as ice, liquid, or vapour, encounters sodium metal (Na), the atoms will be redistributed to give the new substances molecular hydrogen (H2) and sodium hydroxide (NaOH). By this, we know that a chemical change or reaction has occurred.Historical OverviewThe concept of a chemical reaction dates back about 250 years. It had its origins in early experiments that classified substances as elements and compounds and in theories that explained these processes. Development of the concept of a chemical reaction had a primary role in defining the science of chemistry as it is known now .The first substantive studies in this area were on gases. The identification of oxygen in the 18th century by Swedish chemist Carl Wilhelm Scheele and English clergyman Joseph Priestley had particular significance. The influence of French chemist Antoine-Laurent Lavoisier was especially notable, in that his insights confirmed the importance of quantitative measurements of chemical processes. In his book Traité élémentaire de chimie (1789; Elementary Treatise on Chemistry), Lavoisier identified 33 “elements”—substances not broken down into simpler entities. Among his many discoveries, Lavoisier accurately measured the weight gained when elements were oxidized, and he ascribed the result to the combining of the element with oxygen. The concept of chemical reactions involving the combination of elements clearly emerged from his writing, and his approach led others to pursue experimental chemistry as a quantitative science.The other occurrence of historical significance concerning chemical reactions was the development of atomic theory. For this, much credit goes to English chemist John Dalton, who postulated his atomic theory early in the 19th century. Dalton maintained that matter is composed of small, indivisible particles, that the particles, or atoms, of each element were unique, and that chemical reactions were involved in rearranging atoms to form new substances. This view of chemical reactions accurately defines the current subject. Dalton’s theory provided a basis for understanding the results of earlier experimentalists, including the law of conservation of matter (matter is neither created nor destroyed) and the law of constant composition (all samples of a substance have identical elemental compositions).Thus, experiment and theory, the two cornerstones of chemical science in the modern world, together defined the concept of chemical reactions. Now the experimental chemistry provides innumerable examples, and theoretical chemistry allows an understanding of their meaning.Basic Concepts Of Chemical ReactionsSynthesisWhen making a new substance from other substances, chemists say either that they carry out a synthesis or that they synthesize the new material. Reactants are converted to products, and the process is symbolized by a chemical equation. For example, iron (Fe) and sulfur (S) combine to form iron sulfide (FeS).Fe(s) + S(s) → FeS(s)The plus sign indicates that iron reacts with sulfur. The arrow signifies that the reaction “forms” or “yields” iron sulfide, the product. The state of matter of reactants and products is designated with the symbols (s) for solids, (l) for liquids, and (g) for gases.The conservation of matterIn reactions under normal laboratory conditions, matter is neither created nor destroyed, and elements are not transformed into other elements. Therefore, equations depicting reactions must be balanced; that is, the same number of atoms of each kind must appear on opposite sides of the equation. The balanced equation for the iron-sulfur reaction shows that one iron atom can react with one sulfur atom to give one formula unit of iron sulfide.Chemists ordinarily work with weighable quantities of elements and compounds. For example, in the iron-sulfur equation the symbol Fe represents 55.845 grams of iron, S represents 32.066 grams of sulfur, and FeS represents 87.911 grams of iron sulfide. Because matter is not created or destroyed in a chemical reaction, the total mass of reactants is the same as the total mass of products. If some other amount of iron is used, say, one-tenth as much (5.585 grams), only one-tenth as much sulfur can be consumed (3.207 grams), and only one-tenth as much iron sulfide is produced (8.791 grams). If 32.066 grams of sulfur were initially present with 5.585 grams of iron, then 28.859 grams of sulfur would be left over when the reaction was complete.The reaction of methane (CH4, a major component of natural gas) with molecular oxygen (O2) to produce carbon dioxide (CO2) and water can be depicted by the chemical equationCH4(g) + 2O2(g) → CO2(g) + 2H2O(l)Here another feature of chemical equations appears. The number 2 preceding O2 and H2O is a stoichiometric factor. (The number 1 preceding CH4 and CO2 is implied.) This indicates that one molecule of methane reacts with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water. The equation is balanced because the same number of atoms of each element appears on both sides of the equation (here one carbon, four hydrogen, and four oxygen atoms). Analogously with the iron-sulfur example, we can say that 16 grams of methane and 64 grams of oxygen will produce 44 grams of carbon dioxide and 36 grams of water. That is, 80 grams of reactants will lead to 80 grams of products.The ratio of reactants and products in a chemical reaction is called chemical stoichiometry. Stoichiometry depends on the fact that matter is conserved in chemical processes, and calculations giving mass relationships are based on the concept of the mole. One mole of any element or compound contains the same number of atoms or molecules, respectively, as one mole of any other element or compound. By international agreement, one mole of the most common isotope of carbon (carbon-12) has a mass of exactly 12 grams (this is called the molar mass) and represents 6.023×10^23 atoms (Avogadro’s number). One mole of iron contains 55.84 grams; one mole of methane contains 16.04 grams; one mole of molecular oxygen is equivalent to 31.99 grams; and one mole of water is 18.015 grams. Each of these masses represents 6.023× 10^23 molecules.Energy considerationsEnergy plays a key role in chemical processes. According to the modern view of chemical reactions, bonds between atoms in the reactants must be broken, and the atoms or pieces of molecules are reassembled into products by forming new bonds. Energy is absorbed to break bonds, and energy is evolved as bonds are made. In some reactions the energy required to break bonds is larger than the energy evolved on making new bonds, and the net result is the absorption of energy. Such a reaction is said to be endothermic if the energy is in the form of heat. The opposite of endothermic is exothermic; in an exothermic reaction, energy as heat is evolved. The more general terms exoergic (energy evolved) and endoergic (energy required) are used when forms of energy other than heat are involved.A great many common reactions are exothermic. The formation of compounds from the constituent elements is almost always exothermic. Formation of water from molecular hydrogen and oxygen and the formation of a metal oxide such as calcium oxide (CaO) from calcium metal and oxygen gas are examples. Among widely recognizable exothermic reactions is the combustion of fuels (such as the reaction of methane with oxygen mentioned previously).The formation of slaked lime (calcium hydroxide, Ca(OH)2) when water is added to lime (CaO) is exothermic .CaO(s) + H2O (l) → Ca(OH)2(s)This reaction occurs when water is added to dry portland cement to make concrete, and heat evolution of energy as heat is evident because the mixture becomes warm.Not all reactions are exothermic (or exoergic). A few compounds, such as nitric oxide (NO) and hydrazine (N2H4), require energy input when they are formed from the elements. The decomposition of limestone (CaCO3) to make lime (CaO) is also an endothermic process; it is necessary to heat limestone to a high temperature for this reaction to occur.CaCO3(s) → CaO(s) + CO2(g)The decomposition of water into its elements by the process of electrolysis is another endoergicprocess.Electrical energy is used rather than heat energy to carry out this reaction.2 H2O(g) → 2 H2(g) + O2(g)Generally, evolution of heat in a reaction favours the conversion of reactants to products. However, entropy is important in determining the favourability of a reaction.Entropy is a measure of the number of ways in which energy can be distributed in any system. Entropy accounts for the fact that not all energy available in a process can be manipulated to do work.A chemical reaction will favour the formation of products if the sum of the changes in entropy for the reaction system and its surroundings is positive. An example is burning wood. Wood has a low entropy. When wood burns, it produces ash as well as the high-entropy substances carbon dioxide gas and water vapour. The entropy of the reacting system increases during combustion. Just as important, the heat energy transferred by the combustion to its surroundings increases the entropy in the surroundings owing to the heat transferred to it by the exothermic reaction. Again because of the overall increase in entropy, the combustion of hydrogen is product-favoured.Kinetic considerationsChemical reactions commonly need an initial input of energy to begin the process. Although the combustion of wood, paper, or methane is an exothermic process, a burning match or a spark is needed to initiate this reaction. The energy supplied by a match arises from an exothermic chemical reaction that is itself initiated by the frictional heat generated by rubbing the match on a suitable surface.In some reactions, the energy to initiate a reaction can be provided by light. Numerous reactions in Earth’s atmosphere are photochemical, or light-driven, reactions initiated by solar radiation. One example is the transformation of ozone (O3) into oxygen (O2) in the troposphere. The absorption of ultraviolet light (hν) from the Sun to initiate this reaction prevents potentially harmful high-energy radiation from reaching Earth’s surface.For a reaction to occur, it is not sufficient that it be energetically product-favoured. The reaction must also occur at an observable rate. Several factors influence reaction rates, including the concentrations of reactants, the temperature, and the presence of catalysts. The concentration affects the rate at which reacting molecules collide, a prerequisite for any reaction.Temperature is influential because reactions occur only if collisions between reactant molecules are sufficiently energetic. The proportion of molecules with sufficient energy to react is related to the temperature.Catalysts affect rates by providing a lower energy pathway by which a reaction can occur. Among common catalysts are precious metal compounds used in automotive exhaust systems that accelerate the breakdown of pollutants such as nitrogen dioxide into harmless nitrogen and oxygen. A wide array of biochemical catalysts are also known, including chlorophyll in plants (which facilitates the reaction by which atmospheric carbon dioxide is converted to complex organic molecules such as glucose) and many biochemical catalysts called enzymes. The enzyme pepsin, for example, assists in the breakup of large protein molecules during digestion.Classifying Chemical ReactionsChemists classify reactions in a number of ways: (a) by the type of product, (b) by the types of reactants, (c) by reaction outcome, and (d) by reaction mechanism. Often, a given reaction can be placed in two or even three categories.Classification by type of productGas-forming reactionsMany reactions produce a gas such as carbon dioxide, hydrogen sulfide (H2S), ammonia (NH3), or sulfur dioxide (SO2). An example of a gas-forming reaction is that which occurs when a metal carbonate such as calcium carbonate (CaCO3, the chief component of limestone, seashells, and marble) is mixed with hydrochloric acid (HCl) to produce carbon dioxide.CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O (l)In this equation, the symbol (aq) signifies that a compound is in an aqueous, or water, solution.Cake-batter rising is caused by a gas-forming reaction between an acid and baking soda, sodium hydrogen carbonate (sodium bicarbonate, NaHCO3). Tartaric acid (C4H6O6), an acid found in many foods, is often the acidic reactant.C4H6O6(aq) + NaHCO3(aq) → NaC4H5O6(aq) + H2O (l) + CO2(g)In this equation, NaC4H5O6 is sodium tartrate.Most baking powders contain both tartaric acid and sodium hydrogen carbonate, which are kept apart by using starch as a filler. When baking powder is mixed into the moist batter, the acid and sodium hydrogen carbonate dissolve slightly, which allows them to come into contact and react. Carbon dioxide is produced, and the batter rises.Precipitation reactionsFormation of an insoluble compound will sometimes occur when a solution containing a particular cation (a positively charged ion) is mixed with another solution containing a particular anion (a negatively charged ion). The solid that separates is called a precipitate.Classification by types of reactantsTwo types of reactions involve transfer of a charged species. Oxidation-reduction reactions occur with electron transfer between reagents. In contrast, reactions of acids with bases in water involve proton (H+) transfer from an acid to a base.Oxidation-reduction reactionsOxidation-reduction (redox) reactions involve the transfer of one or more electrons from a reducing agent to an oxidizing agent. This has the effect of reducing the real or apparent electric charge on an atom in the substance being reduced and of increasing the real or apparent electric charge on an atom in the substance being oxidized. Simple redox reactions include the reactions of an element with oxygen. For example, magnesium burns in oxygen to form magnesium oxide (MgO). The product is an ionic compound, made up of Mg2+ and O2− ions. The reaction occurs with each magnesium atom giving up two electrons and being oxidized and each oxygen atom accepting two electrons and being reduced.Another common redox reaction is one step in the rusting of iron in damp air.2Fe(s) + 2H2O(l) + O2(g) → 2Fe(OH)2(s)Here iron metal is oxidized to iron dihydroxide (Fe(OH)2); elemental oxygen (O2) is the oxidizing agent.Redox reactions are the source of the energy of batteries. The electric current generated by a battery arises because electrons are transferred from a reducing agent to an oxidizing agent through the external circuitry. In a common dry cell and in alkaline batteries, two electrons per zinc atom are transferred to the oxidizing agent, thereby converting zinc metal to the Zn2+ ion. In dry-cell batteries, which are often used in flashlights, the electrons given up by zinc are taken up by ammonium ions (NH4+) present in the battery as ammonium chloride (NH4Cl). In alkaline batteries, which are used in calculators and watches, the electrons are transferred to a metal oxide such as silver oxide (AgO), which is reduced to silver metal in the process.Acid-base reactionsAcids and bases are important compounds in the natural world, so their chemistry is central to any discussion of chemical reactions. There are several theories of acid-base behaviour.The Arrhenius theoryThe Arrhenius theory, named after Swedish physicist Svante August Arrhenius, views an acid as a substance that increases the concentration of the hydronium ion (H3O+) in an aqueous solution and a base as a substance that increases the hydroxide ion (OH−) concentration. Well-known acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), and acetic acid (CH3COOH). Bases includes such common substances as caustic soda (sodium hydroxide, NaOH) and slaked lime (calcium hydroxide, Ca(OH)2). Another common base is ammonia (NH3), which reacts with water to give a basic solution according to the following balanced equation.NH3(aq) + H2O(l) → NH4+(aq) + OH−(aq)(This reaction occurs to a very small extent; the hydroxide ion concentration is small but measurable.)A large number of natural bases are known, including morphine, cocaine, nicotine, and caffeine; many synthetic drugs are also bases. All of these contain a nitrogen atom bonded to three other groups, and all behave similarly to ammonia in that they can react with water to give a solution containing the hydroxide ion.Amino acids, a very important class of compounds, are able to function both as acids and as bases. Amino acid molecules contain both acidic (―COOH) and basic (―NH2) sites. In an aqueous solution, amino acids exist in both the molecular form and the so-called "zwitterionic" form, H3N + CH2CO2−. In this structure the nitrogen atom bears a positive charge, and the oxygen atom of the acid group bears a negative charge.According to the Arrhenius theory, acid-base reactions involve the combination of the hydrogen ion (H+) and the hydroxide ion to form water. An example is the reaction of aqueous solutions of sodium hydroxide and hydrochloric acid.HCl(aq) + NaOH(aq) → NaCl(aq) + H2O (l)The Brønsted-Lowry theoryA somewhat more general acid-base theory, the Brønsted-Lowry theory, named after Danish chemist Johannes Nicolaus Brønsted and English chemist Thomas Martin Lowry, defines an acid as a proton donor and a base as a proton acceptor. In this theory, the reaction of an acid and base is represented as an equilibrium reaction.acid (1) + base (2) ⇌ base (1) + acid (2)(The double arrows, ⇌, indicate that the products can re-form the reactants in a dynamic process.)The Lewis theoryA still broader acid and base theory was proposed by American physical chemist Gilbert Newton Lewis. In the Lewis theory, bases are defined as electron-pair donors and acids as electron-pair acceptors. Acid-base reactions involve the combination of the Lewis acid and base through sharing of the base’s electron pair.Ammonia is an example of a Lewis base.Classification by reaction outcomeChemists often classify reactions on the basis of the overall result. Here several commonly encountered reactions are classified. As previously noted, many reactions defy simple classification and may fit in several categories.Decomposition reactionsDecomposition reactions are processes in which chemical species break up into simpler parts. Usually, decomposition reactions require energy input. For example, a common method of producing oxygen gas in the laboratory is the decomposition of potassium chlorate (KClO3) by heat.2KClO3(s) → 2KCl(s) + 3O2(g)Another decomposition reaction is the production of sodium (Na) and chlorine (Cl2) by electrolysis of molten sodium chloride (NaCl) at high temperature.2NaCl (l) → 2Na (l) + Cl2(g)A decomposition reaction that was very important in the history of chemistry is the decomposition of mercury oxide (HgO) with heat to give mercury metal (Hg) and oxygen gas. This is the reaction used by 18th-century chemists Carl Wilhelm Scheele, Joseph Priestley, and Antoine-Laurent Lavoisier in their experiments on oxygen.2HgO(s) → 2Hg (l) + O2(g)Polymerization reactionsPolymers are high-molecular-weight compounds, fashioned by the aggregation of many smaller molecules called monomers. The plastics that have so changed society and the natural and synthetic fibres used in clothing are polymers. There are two basic ways to form polymers: (a) linking small molecules together, a type of addition reaction, and (b) combining two molecules (of the same or different type) with the elimination of a stable small molecule such as water. This latter type of polymerization combines addition and elimination reactions and is called a condensation reaction .Classification by reaction mechanismReaction mechanisms provide details on how atoms are shuffled and reassembled in the formation of products from reactants. Chain and photolysis reactions are named on the basis of the mechanism of the process.Chain reactionsChain reactions occur in a sequence of steps, in which the product of each step is a reagent for the next. Chain reactions generally involve three distinct processes: an initiation step that begins the reaction, a series of chain-propagation steps, and, eventually, a termination step.Polymerization reactions are chain reactions, and the formation of Teflon from tetrafluoroethylene is one example. In this reaction, a peroxide (a compound in which two oxygen atoms are joined together by a single covalent bond) may be used as the initiator . Peroxides readily form highly reactive free-radical species (a species with an unpaired electron) that initiate the reaction. There are a number of different ways to terminate the chain, only one of which is shown. (In the following equations, the dots represent unpaired electrons, and R is a generic organic group.)Decomposition of a peroxide to radicals:ROOR → 2 RO∙Chain initiation:RO∙ + F2C=CF2 → ROCF2CF2∙Chain-propagation steps:ROCF2CF2∙ + F2C=CF2 → ROCF2CF2CF2CF2∙ROCF2CF2CF2CF2∙ + (n−2)F2C=CF2 → RO―(CF2CF2∙)n―A possible chain-termination step:RO―(CF2CF2∙)n― + ∙OR → RO(CF2CF2)nORPhotolysis reactionsPhotolysis reactions are initiated or sustained by the absorption of electromagnetic radiation. One example, the decomposition of ozone to oxygen in the atmosphere, is mentioned above in the section Kinetic considerations. Another example is the synthesis of chloromethane from methane and chlorine, which is initiated by light. The overall reaction isCH4(g) + Cl2(g) + hυ → CH3Cl(g) + HCl(g),where hυ represents light. This reaction, coincidentally, is also a chain reaction. It begins with the endothermic reaction of a chlorine molecule (Cl2) to give chlorine atoms, a process that occurs under ultraviolet irradiation. When formed, some of the chlorine atoms recombine to form chlorine molecules, but not all do so. If a chlorine atom instead collides with a methane molecule, a two-step chain propagation occurs. The first propagation step produces the methyl radical (CH3). This free-radical species reacts with a chlorine molecule to give the product and a chlorine atom, which continues the chain reaction for many additional steps. Possible termination steps include combination of two methyl radicals to form ethane (CH3CH3) and a combination of methyl and chlorine radicals to give chloromethane.Thanks for Watching Please Upvotes and share with your friends and followersGrasp ScienceDivyanshu Upadhyay